Enhancing Cation Diffusion and Suppressing Anion Diffusion via Lewis-Acidic Polymer Electrolytes.

PubMed

Savoie, Brett M; Webb, Michael A; Miller, Thomas F

2017-02-02

Solid polymer electrolytes (SPEs) have the potential to increase both the energy density and stability of lithium-based batteries, but low Li + conductivity remains a barrier to technological viability. SPEs are designed to maximize Li + diffusivity relative to the anion while maintaining sufficient salt solubility. It is thus remarkable that poly(ethylene oxide) (PEO), the most widely used SPE, exhibits Li + diffusivity that is an order of magnitude smaller than that of typical counterions at moderate salt concentrations. We show that Lewis-basic polymers like PEO favor slow cation and rapid anion diffusion, while this relationship can be reversed in Lewis-acidic polymers. Using molecular dynamics, polyboranes are identified that achieve up to 10-fold increases in Li + diffusivities and significant decreases in anion diffusivities, relative to PEO in the dilute-ion regime. These results illustrate a general principle for increasing Li + diffusivity and transference number with chemistries that exhibit weaker cation and stronger anion coordination.

The diffusion dynamics of PEGylated liposomes in the intact vitreous of the ex vivo porcine eye: A fluorescence correlation spectroscopy and biodistribution study.

PubMed

Eriksen, Anne Z; Brewer, Jonathan; Andresen, Thomas L; Urquhart, Andrew J

2017-04-30

The diffusion dynamics of nanocarriers in the vitreous and the influence of nanocarrier physicochemical properties on these dynamics is an important aspect of the efficacy of intravitreal administered nanomedicines for the treatment of posterior segment eye diseases. Here we use fluorescence correlation spectroscopy (FCS) to determine liposome diffusion coefficients in the intact vitreous (D Vit ) of ex vivo porcine eyes using a modified Miyake-Apple technique to minimize the disruption of the vitreous fine structure. We chose to investigate whether the zeta potential of polyethylene glycol functionalized (i.e. PEGylated) liposomes altered liposome in situ diffusion dynamics in the vitreous. Non-PEGylated cationic nanocarriers have previously shown little to no diffusion in the vitreous, whilst neutral and anionic have shown diffusion. The liposomes investigated had diameters below 150nm and zeta potentials ranging from -20 to +12mV. We observed that PEGylated cationic liposomes had significantly lower D Vit values (1.14μm 2 s -1 ) than PEGylated neutral and anionic liposomes (2.78 and 2.87μm 2 s -1 ). However, PEGylated cationic liposomes had a similar biodistribution profile across the vitreous to the other systems. These results show that PEGylated cationic liposomes with limited cationic charge can diffuse across the vitreous and indicate that the vitreous as a barrier to nanocarriers (Ø<500nm) is more complicated than simply an electrostatic barrier as previously suggested. Copyright © 2017 Elsevier B.V. All rights reserved.

Nanoscale oxidation and complex oxide growth on single crystal iron surfaces and external electric field effects.

PubMed

Jeon, Byoungseon; Van Overmeere, Quentin; van Duin, Adri C T; Ramanathan, Shriram

2013-02-14

Oxidation of iron surfaces and oxide growth mechanisms have been studied using reactive molecular dynamics. Oxide growth kinetics on Fe(100), (110), and (111) surface orientations has been investigated at various temperatures and/or an external electric field. The oxide growth kinetics decreases in the order of (110), (111), and (100) surfaces at 300 K over 1 ns timescale while higher temperature increases the oxidation rate. The oxidation rate shows a transition after an initial high rate, implying that the oxide formation mechanism evolves, with iron cation re-ordering. In early stages of surface oxide growth, oxygen transport through iron interstitial sites is dominant, yielding non-stoichiometric wüstite characteristics. The dominant oxygen inward transport decreases as the oxide thickens, evolving into more stoichiometric oxide phases such as wüstite or hematite. This also suggests that cation outward transport increases correspondingly. In addition to oxidation kinetics simulations, formed oxide layers have been relaxed in the range of 600-1500 K to investigate diffusion characteristics, fitting these results into an Arrhenius relation. The activation energy of oxygen diffusion in oxide layers formed on Fe(100), (110), and (111) surfaces was estimated to be 0.32, 0.26, and 0.28 eV, respectively. Comparison between our modeling results and literature data is then discussed. An external electric field (10 MV cm(-1)) facilitates initial oxidation kinetics by promoting oxygen transport through iron lattice interstitial sites, but reaches self-limiting thickness, showing that similar oxide formation stages are maintained when cation transport increases. The effect of the external electric field on iron oxide structure, composition, and oxide activation energy is found to be minimal, whereas cation outward migration is slightly promoted.

Diffusion of cations in chromia layers grown on iron-base alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lobnig, R.E.; Hennesen, K.; Grabke, H.J.

Diffusion of the cations Cr, Fe, Mn, and Ni in Cr{sub 2}O{sub 3} has been investigated at 1,173 K. The diffusion measurements were performed on chromia layers grown on the model alloys Fe-20Cr and Fe-20Cr-12Ni in order to consider effects of small amounts of dissolved alien cations in Cr{sub 2}O{sub 3}. The samples were diffusion annealed in H{sub 2}-H{sub 2}O at an oxygen partial pressure close to the Cr{sub 2}O{sub 3}/Cr equilibrium. For all tracers the lattice-diffusion coefficients are 3-5 orders of magnitude smaller than the grain-boundary diffusion coefficients. The lattice diffusivity of Mn is about two orders of magnitudemore » greater than the other lattice-diffusion coefficients, especially in Cr{sub 2}O{sub 3} grown on Fe-20Cr-12Ni. The values of the diffusion coefficients for Cr, Fe, and Ni are in the same range. Diffusion of the tracers in Cr{sub 2}O{sub 3} grown on different alloys did not show significant differences with the exception of Mn.« less

Molecular dynamics simulation of diffusion and electrical conductivity in montmorillonite interlayers

DOE PAGES

Greathouse, Jeffery A.; Cygan, Randall T.; Fredrich, Joanne T.; ...

2016-01-20

In this study, the diffusion of water and ions in the interlayer region of smectite clay minerals represents a direct probe of the type and strength of clay–fluid interactions. Interlayer diffusion also represents an important link between molecular simulation and macroscopic experiments. Here we use molecular dynamics simulation to investigate trends in cation and water diffusion in montmorillonite interlayers, looking specifically at the effects of layer charge, interlayer cation and cation charge (sodium or calcium), water content, and temperature. For Na-montmorillonite, the largest increase in ion and water diffusion coefficients occurs between the one-layer and two-layer hydrates, corresponding to themore » transition from inner-sphere to outer-sphere surface complexes. Calculated activation energies for ion and water diffusion in Na-montmorillonite are similar to each other and to the water hydrogen bond energy, suggesting the breaking of water–water and water–clay hydrogen bonds as a likely mechanism for interlayer diffusion. A comparison of interlayer diffusion with that of bulk electrolyte solutions reveals a clear trend of decreasing diffusion coefficient with increasing electrolyte concentration, and in most cases the interlayer diffusion results are nearly coincident with the corresponding bulk solutions. Trends in electrical conductivities computed from the ion diffusion coefficients are also compared.« less

Dependence of Ion Dynamics on the Polymer Chain Length in Poly(ethylene oxide)-Based Polymer Electrolytes.

PubMed

Chattoraj, Joyjit; Knappe, Marisa; Heuer, Andreas

2015-06-04

It is known from experiments that in the polymer electrolyte system, which contains poly(ethylene oxide) chains (PEO), lithium-cations (Li(+)), and bis(trifluoromethanesulfonyl)imide-anions (TFSI(-)), the cation and the anion diffusion and the ionic conductivity exhibit a similar chain-length dependence: with increasing chain length, they start dropping steadily, and later, they saturate to constant values. These results are surprising because Li-cations are strongly correlated with the polymer chains, whereas TFSI-anions do not have such bonding. To understand this phenomenon, we perform molecular dynamics simulations of this system for four different polymer chain lengths. The diffusion results obtained from our simulations display excellent agreement with the experimental data. The cation transport model based on the Rouse dynamics can successfully quantify the Li-diffusion results, which correlates Li diffusion with the polymer center-of-mass motion and the polymer segmental motion. The ionic conductivity as a function of the chain length is then estimated based on the chain-length-dependent ion diffusion, which shows a temperature-dependent deviation for short chain lengths. We argue that in the first regime, counterion correlations modify the conductivity, whereas for the long chains, the system behaves as a strong electrolyte.

Trends in Effective Diffusion Coefficients for Ion-exchange Strengthening of Soda Lime Silicate Glasses

NASA Astrophysics Data System (ADS)

Karlsson, Stefan; Wondraczek, Lothar; Ali, Sharafat; Jonson, Bo

2017-04-01

Monovalent cations enable efficient ion exchange processes due to their high mobility in silicate glasses. Numerous properties can be modified in this way, e.g., mechanical, optical, electrical or chemical performance. In particular, alkali cation exchange has received significant attention, primarily with respect to introducing compressive stress into the surface region of a glass, which increases mechanical durability. However, most of the present applications rely on specifically tailored matrix compositions in which the cation mobility is enhanced. This largely excludes the major area of soda lime silicates (SLS) such as are commodity in almost all large-scale applications of glasses. Basic understanding of the relations between structural parameters and the effective diffusion coefficients may help to improve ion-exchanged SLS glass products, on the one hand in terms of obtainable strength and on the other in terms of cost. In the present paper, we discuss the trends in the effective diffusion coefficients when exchanging Na+ for various monovalent cations (K+, Cu+, Ag+, Rb+ and Cs+) by drawing relations to physico-chemical properties. Correlations of effective diffusion coefficients were found for the bond dissociation energy and the electronic cation polarizability, indicating that localization and rupture of bonds are of importance for the ion exchange rate.

Role of charge screening and delocalization for lipophilic cation permeability of model and mitochondrial membranes.

PubMed

Trendeleva, Tatiana A; Sukhanova, Evgenia I; Rogov, Anton G; Zvyagilskaya, Renata A; Seveina, Inna I; Ilyasova, Tatiana M; Cherepanov, Dmitry A; Skulachev, Vladimir P

2013-09-01

The effects of the mitochondria-targeted lipophilic cation dodecyltriphenylphosphonium (C12TPP, the charge is delocalized and screened by bulky hydrophobic residues) and those of lipophilic cations decyltriethylammonium bromide and cetyltrimethylammonium bromide (C10TEA and C16TMA, the charges are localized and screened by less bulky residues) on bilayer planar phospholipid membranes and tightly-coupled mitochondria from the yeast Yarrowia lipolytica have been compared. In planar membranes, C12TPP was found to generate a diffusion potential as if it easily penetrates these membranes. In the presence of palmitate, C12TPP induced H(+) permeability like plastoquinonyl decyltriphenilphosphonium that facilitates transfer of fatty acid anions (Severin et al., PNAS, 2010, 107, 663-668). C12TPP was shown to stimulate State 4 respiration of mitochondria and caused a mitochondrial membrane depolarization with a half-maximal effect at 6μM. Besides, C12TPP profoundly potentiated the uncoupling effect of endogenous or added fatty acids. C10TEA and C16TMA inhibited State 4 respiration and decreased the membrane potential, though at much higher concentrations than C12TPP, and they did not promote the uncoupling action of fatty acids. These relationships were modeled by molecular dynamics. They can be explained by different membrane permeabilities for studied cations, which in turn are due to different availabilities of the positive charge in these cations to water dipoles. Copyright © 2012 Elsevier B.V. All rights reserved.

Theoretical and experimental studies of water interaction in acetate based ionic liquids.

PubMed

Shi, Wei; Damodaran, Krishnan; Nulwala, Hunaid B; Luebke, David R

2012-12-05

Water interactions in 1-ethyl-3-methylimidazolium acetate ([emim][CH(3)COO]) were studied utilizing classical and ab initio simulation methods. The self-diffusivities for water and the ionic liquid (IL) were studied experimentally using pulse field gradient NMR spectroscopy and correlated with computational results. Water forms hydrogen bonding networks with the ionic liquid, and depending on the concentration of water, there are profound effects on the self-diffusivities of the various species. Both simulation and experiments show that the self-diffusivities for species in the water-[emim][CH(3)COO] system exhibit minima at 40-50 mol% water. Water interaction with the [CH(3)COO](-) anion predominates over the water-water and water-cation interactions at most water concentrations. Simulations further indicate that decreasing water-[CH(3)COO](-) interaction will increase the IL and water self-diffusivities. Self-diffusivities in the water-IL systems are dependent upon the cation in a complex way. Water interactions with [P(4444)][CH(3)COO] are reduced compared to [emim][CH(3)COO]. The [P(4444)](+) cation is bulkier than the [emim](+) cation and has a smaller self-diffusivity, but when water was introduced to [P(4444)] [CH(3)COO], the water-[CH(3)COO](-) hydrogen bonding network in the [P(4444)][CH(3)COO] was much smaller than the one observed in [emim][CH(3)COO].

Genome-Wide Identification and Expression Analysis of the Cation Diffusion Facilitator Gene Family in Turnip Under Diverse Metal Ion Stresses.

PubMed

Li, Xiong; Wu, Yuansheng; Li, Boqun; He, Wenqi; Yang, Yonghong; Yang, Yongping

2018-01-01

The cation diffusion facilitator (CDF) family is one of the gene families involved in metal ion uptake and transport in plants, but the understanding of the definite roles and mechanisms of most CDF genes remain limited. In the present study, we identified 18 candidate CDF genes from the turnip genome and named them BrrMTP1.1 - BrrMTP12 . Then, we performed a comparative genomic analysis on the phylogenetic relationships, gene structures and chromosome distributions, conserved domains, and motifs of turnip CDFs. The constructed phylogenetic tree indicated that the BrrMTPs were divided into seven groups (groups 1, 5, 6, 7, 8, 9, and 12) and formed three major clusters (Zn-CDFs, Fe/Zn-CDFs, and Mn-CDFs). Moreover, the structural characteristics of the BrrMTP members in the same group were similar but varied among groups. To investigate the potential roles of BrrMTPs in turnip, we conducted an expression analysis on all BrrMTP genes under Mg, Zn, Cu, Mn, Fe, Co, Na, and Cd stresses. Results showed that the expression levels of all BrrMTP members were induced by at least one metal ion, indicating that these genes may be related to the tolerance or transport of those metal ions. Based on the roles of different metal ions for plants, we hypothesized that BrrMTP genes are possibly involved in heavy metal accumulation and tolerance to salt stress apart from their roles in the maintenance of mineral nutrient homeostasis in turnip. These findings are helpful to understand the roles of MTPs in plants and provide preliminary information for the study of the functions of BrrMTP genes.

Mn-euvering manganese: the role of transporter gene family members in manganese uptake and mobilization in plants

PubMed Central

Socha, Amanda L.; Guerinot, Mary Lou

2014-01-01

Manganese (Mn), an essential trace element, is important for plant health. In plants, Mn serves as a cofactor in essential processes such as photosynthesis, lipid biosynthesis and oxidative stress. Mn deficient plants exhibit decreased growth and yield and are more susceptible to pathogens and damage at freezing temperatures. Mn deficiency is most prominent on alkaline soils with approximately one third of the world's soils being too alkaline for optimal crop production. Despite the importance of Mn in plant development, relatively little is known about how it traffics between plant tissues and into and out of organelles. Several gene transporter families have been implicated in Mn transport in plants. These transporter families include NRAMP (natural resistance associated macrophage protein), YSL (yellow stripe-like), ZIP (zinc regulated transporter/iron-regulated transporter [ZRT/IRT1]-related protein), CAX (cation exchanger), CCX (calcium cation exchangers), CDF/MTP (cation diffusion facilitator/metal tolerance protein), P-type ATPases and VIT (vacuolar iron transporter). A combination of techniques including mutant analysis and Synchrotron X-ray Fluorescence Spectroscopy can assist in identifying essential transporters of Mn. Such knowledge would vastly improve our understanding of plant Mn homeostasis. PMID:24744764

Compositional and Ionic-Size Controls on the Diffusion of Divalent Cations in Garnet: Insights from Atomistic Simulations

NASA Astrophysics Data System (ADS)

Carlson, W. D.

2012-12-01

Divalent cations in garnet (Mg, Fe, Mn, Ca) diffuse at rates that depend strongly on the host-crystal composition and on the ionic radius of the diffusant. Understanding of the nanoscale basis for these behaviors comes from atomistic simulations that calculate energies in the static limit for the defects and transition-state configurations associated with each diffusive step. Diffusion of divalent cations requires (a) creation of a cation-vacancy defect in a dodecahedral site and of a charge-compensating oxygen-vacancy defect that may or may not be in close spatial association; (b) except in the case of self-diffusion, creation of an impurity defect in which a foreign atom replaces the normal atom in a dodecahedral site adjacent to the vacancy; and (c) during the diffusive process, motion of the diffusing atom to a 'saddlepoint' position that represents the transition-state configuration. Comparisons of the system's energy in these various states, in structures of different composition and for ions of different ionic size, allows assessment of the nanoscale controls on diffusion kinetics. Molecular-statics calculations quantify defect energies and identify the transition-state configuration: the maximum energy along the diffusion path between two adjacent dodecahedral sites results when the diffusing ion is surrounded symmetrically by the six oxygen atoms that lie between the two sites. Across the range of end-member compositions, self-diffusion coefficients measured at identical conditions, and the tracer diffusivity of a single ion measured at identical conditions, can each vary by five orders of magnitude or more. Measured activation energies for these motions, however, are all equivalent to within ±6%. Calculated activation energies are in agreement with observations, in that they vary by only ±10%. Calculated vacancy-formation energies, on the other hand, are significantly larger in expanded structures; for example, that energy is greater for Prp than for Grs by ~ 470 kJ/mol. Thus in expanded structures, much higher vacancy concentrations can be produced at the same energetic cost, greatly enhancing rates of diffusion. The primary explanation for the more rapid diffusion of divalent cations in structures with larger cell dimensions therefore comes not from reduced saddlepoint strain energies in more compliant structures, but instead from the smaller energy required to create vacancy defects. Diffusivities of divalent cations exhibit a curious parabolic dependence on ionic size: for each structure, an optimally-sized ion exists, close in size to the dominant ion, that exhibits the fastest diffusion. Larger ions — and enigmatically, smaller ions — both diffuse more slowly. Calculated impurity-defect energies show that undersized impurity ions are bound more tightly in their sites, but the effects are too small in comparison to corresponding reductions in strain energy for the transition-state configuration to account for observed rate differences. Calculated vacancy-association energies reveal a slight tendency for vacancies to associate preferentially with larger impurity ions, but again the effect appears to be too small to provide a full explanation for observed behaviors.

An unusual slowdown of fast diffusion in a room temperature

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chathoth,; Mamontov, Eugene; Fulvio, Pasquale F

2013-01-01

Using quasielastic neutron scattering in the temperature range from 290 to 350 K, we show that the diffusive motions in a room temperature ionic liquid [H2NC(dma)2][BETI] become faster for a fraction of cations when the liquid is confined in a mesoporous carbon. This applies to both the localized and long-range translational diffusive motions of the highly mobile cations, although the former exhibit an unusual trend of slowing-down as the temperature is increased, until the localized diffusivity is reduced to the bulk ionic liquid value at a temperature of 350 K.

Enhanced desorption of cesium from collapsed interlayer regions in vermiculite by hydrothermal treatment with divalent cations.

PubMed

Yin, Xiangbiao; Wang, Xinpeng; Wu, Hao; Ohnuki, Toshihiko; Takeshita, Kenji

2017-03-15

Adsorption of cesium (Cs) on phyllosilicates has been intensively investigated because natural soils have strong ability of immobilizing Cs within clay minerals resulting in difficulty of decontamination. The objectives of present study are to clarify how Cs fixation on vermiculite is influenced by structure change caused by Cs sorption at different loading levels and how Cs desorption is affected by various replacing cations induced at different treating temperature. As a result, more than 80% of Cs was readily desorbed from vermiculite with loading amount of 2% saturated Cs (5.49×10 -3 mmolg -1 ) after four cycles of treatment of 0.01M Mg 2+ /Ca 2+ at room temperature, but less than 20% of Cs was desorbed from saturated vermiculite. These distinct desorption patterns were attributed to inhibition of Cs desorption by interlayer collapse of vermiculite, especially at high Cs loadings. In contrast, elevated temperature significantly facilitated divalent cations to efficiently desorb Cs from collapsed regions. After five cycles of treatment at 250°C with 0.01M Mg 2+ , ∼100% removal of saturated Cs was achieved. X-ray diffraction analysis results suggested that Cs desorption was completed through enhanced diffusion of Mg 2+ cations into collapsed interlayer space under hydrothermal condition resulting in subsequent interlayer decollapse and readily release of Cs + . Copyright © 2016 Elsevier B.V. All rights reserved.

Ion transport with charge-protected and non-charge-protected cations using the compensated Arrhenius formalism. Part 2. Relationship between ionic conductivity and diffusion.

PubMed

Petrowsky, Matt; Fleshman, Allison; Bopege, Dharshani N; Frech, Roger

2012-08-09

Temperature-dependent ionic conductivities and cation/anion self-diffusion coefficients are measured for four electrolyte families: TbaTf-linear primary alcohols, LiTf-linear primary alcohols, TbaTf-n-alkyl acetates, and LiTf-n-alkyl acetates. The Nernst-Einstein equation does not adequately describe the data. Instead, the compensated Arrhenius formalism is applied to both conductivity and diffusion data. General trends based on temperature and alkyl chain length are observed when conductivity is plotted against cation or anion diffusion coefficient, but there is no clear pattern to the data. However, plotting conductivity exponential prefactors against those for diffusion results in four distinct curves, one each for the alcohol and acetate families described above. Furthermore, the TbaTf-alcohol and TbaTf-acetate data are "in line" with each other. The conductivity prefactors for the LiTf-alcohol data are smaller than those for the TbaTf data. The LiTf-acetate data have the lowest conductivity prefactors. This trend in prefactors mirrors the observed trend in degree of ionic association for these electrolytes.

Kinetic Monte Carlo Investigation of the Effects of Vacancy Pairing on Oxygen Diffusivity in Yttria-Stabilized Zirconia

NASA Technical Reports Server (NTRS)

Good, Brian S.

2011-01-01

Yttria-stabilized zirconia s high oxygen diffusivity and corresponding high ionic conductivity, and its structural stability over a broad range of temperatures, have made the material of interest for use in a number of applications, for example, as solid electrolytes in fuel cells. At low concentrations, the stabilizing yttria also serves to increase the oxygen diffusivity through the presence of corresponding oxygen vacancies, needed to maintain charge neutrality. At higher yttria concentration, however, diffusivity is impeded by the larger number of relatively high energy migration barriers associated with yttrium cations. In addition, there is evidence that oxygen vacancies preferentially occupy nearest-neighbor sites around either dopant or Zr cations, further affecting vacancy diffusion. We present the results of ab initio calculations that indicate that it is energetically favorable for oxygen vacancies to occupy nearest-neighbor sites adjacent to Y ions, and that the presence of vacancies near either species of cation lowers the migration barriers. Kinetic Monte Carlo results from simulations incorporating this effect are presented and compared with results from simulations in which the effect is not present.

Effect of cation structure on the oxygen solubility and diffusivity in a range of bis{(trifluoromethyl)sulfonyl}imide anion based ionic liquids for lithium-air battery electrolytes.

PubMed

Neale, Alex R; Li, Peilin; Jacquemin, Johan; Goodrich, Peter; Ball, Sarah C; Compton, Richard G; Hardacre, Christopher

2016-04-28

This paper reports on the solubility and diffusivity of dissolved oxygen in a series of ionic liquids (ILs) based on the bis{(trifluoromethyl)sulfonyl}imide anion with a range of related alkyl and ether functionalised cyclic alkylammonium cations. Cyclic voltammetry has been used to observe the reduction of oxygen in ILs at a microdisk electrode and chronoamperometric measurements have then been applied to simultaneously determine both the concentration and the diffusion coefficient of oxygen in different ILs. The viscosity of the ILs and the calculated molar volume and free volume are also reported. It is found that, within this class of ILs, the oxygen diffusivity generally increases with decreasing viscosity of the neat IL. An inverse relationship between oxygen solubility and IL free volume is reported for the two IL families implying that oxygen is not simply occupying the available empty space. In addition, it is reported that the introduction of an ether-group into the IL cation structure promotes the diffusivity of dissolved oxygen but reduces the solubility of the gas.

Energetic and dynamic analysis of transport of Na + and K + through a cyclic peptide nanotube in water and in lipid bilayers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, Yeonho; Lee, Ji Hye; Hwang, Hoon

Potential of mean force (PMF) profiles and position-dependent diffusion coefficients of Na + and K + are calculated to elucidate the translocation of ions through a cyclic peptide nanotube, composed of 8 × cyclo[-(D-Leu-Trp) 4-] rings, in water and in hydrated DMPC bilayers. The PMF profiles and PMF decomposition analysis for the monovalent cations show that favorable interactions of the cations with the CPN as well as the lipid bilayer and dehydration free energy penalties are two major competing factors which determine the free energy surface for ion transport through CPNs both in water and lipid bilayers, and that themore » selectivity of CPNs to cations mainly arises from favorable interaction energies of cations with CPNs and lipid bilayers that are more dominant than the dehydration penalties. Calculations of the position-dependent diffusion coefficients and dynamic friction kernels of the cations indicate that the dehydration process along with the molecular rearrangements occurring outside the channel and the coupling of the ion motions with the chain-structured water movements inside the channel lead to decrease of the diffusion coefficients far away from the channel entrance and also reduced coefficients inside the channel. Here the PMF and diffusivity profiles for Na + and K + reveal that the energetics of ion transport through the CPN are governed by global interactions of ions with all the components in the system while the diffusivity of ions through the channel is mostly determined by local interactions of ions with the confined water molecules inside the channel. Comparison of Na + and K + ion distributions based on overdamped Brownian dynamics simulations based on the PMF and diffusivity profiles with the corresponding results from molecular dynamics shows good agreement, indicating accuracy of the Bayesian inference method for determining diffusion coefficients in this application. In addition this work shows that position-dependent diffusion coefficients of ions are required to explain the dynamics and conductance of ions through the CPN properly.« less

Energetic and dynamic analysis of transport of Na + and K + through a cyclic peptide nanotube in water and in lipid bilayers

DOE PAGES

Song, Yeonho; Lee, Ji Hye; Hwang, Hoon; ...

2016-11-04

Potential of mean force (PMF) profiles and position-dependent diffusion coefficients of Na + and K + are calculated to elucidate the translocation of ions through a cyclic peptide nanotube, composed of 8 × cyclo[-(D-Leu-Trp) 4-] rings, in water and in hydrated DMPC bilayers. The PMF profiles and PMF decomposition analysis for the monovalent cations show that favorable interactions of the cations with the CPN as well as the lipid bilayer and dehydration free energy penalties are two major competing factors which determine the free energy surface for ion transport through CPNs both in water and lipid bilayers, and that themore » selectivity of CPNs to cations mainly arises from favorable interaction energies of cations with CPNs and lipid bilayers that are more dominant than the dehydration penalties. Calculations of the position-dependent diffusion coefficients and dynamic friction kernels of the cations indicate that the dehydration process along with the molecular rearrangements occurring outside the channel and the coupling of the ion motions with the chain-structured water movements inside the channel lead to decrease of the diffusion coefficients far away from the channel entrance and also reduced coefficients inside the channel. Here the PMF and diffusivity profiles for Na + and K + reveal that the energetics of ion transport through the CPN are governed by global interactions of ions with all the components in the system while the diffusivity of ions through the channel is mostly determined by local interactions of ions with the confined water molecules inside the channel. Comparison of Na + and K + ion distributions based on overdamped Brownian dynamics simulations based on the PMF and diffusivity profiles with the corresponding results from molecular dynamics shows good agreement, indicating accuracy of the Bayesian inference method for determining diffusion coefficients in this application. In addition this work shows that position-dependent diffusion coefficients of ions are required to explain the dynamics and conductance of ions through the CPN properly.« less

Structural, Chemical, and Dynamical Frustration: Origins of Superionic Conductivity in closo -Borate Solid Electrolytes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kweon, Kyoung E.; Varley, Joel B.; Shea, Patrick

Li 2B 12H 12, Na 2B 12H 12, and their closo-borate relatives exhibit unusually high ionic conductivity, making them attractive as a new class of candidate electrolytes in solid-state Li- and Na-ion batteries. However, further optimization of these materials requires a deeper understanding of the fundamental mechanisms underlying ultrafast ion conduction. To this end, we use ab initio molecular dynamics simulations and density-functional calculations to explore the motivations for cation diffusion. We find that superionic behavior in Li 2B 12H 12 and Na 2B 12H 12 results from a combination of key structural, chemical, and dynamical factors that introduce intrinsicmore » frustration and disorder. A statistical metric is used to show that the structures exhibit a high density of accessible interstitial sites and site types, which correlates with the flatness of the energy landscape and the observed cation mobility. Furthermore, cations are found to dock to specific anion sites, leading to a competition between the geometric symmetry of the anion and the symmetry of the lattice itself, which can facilitate cation hopping. Finally, facile anion reorientations and other low-frequency thermal vibrations lead to fluctuations in the local potential that enhance cation mobility by creating a local driving force for hopping. In conclusion, we discuss the relevance of each factor for developing new ionic conductivity descriptors that can be used for discovery and optimization of closo-borate solid electrolytes, as well as superionic conductors more generally.« less

Structural, Chemical, and Dynamical Frustration: Origins of Superionic Conductivity in closo -Borate Solid Electrolytes

DOE PAGES

Kweon, Kyoung E.; Varley, Joel B.; Shea, Patrick; ...

2017-10-11

Li 2B 12H 12, Na 2B 12H 12, and their closo-borate relatives exhibit unusually high ionic conductivity, making them attractive as a new class of candidate electrolytes in solid-state Li- and Na-ion batteries. However, further optimization of these materials requires a deeper understanding of the fundamental mechanisms underlying ultrafast ion conduction. To this end, we use ab initio molecular dynamics simulations and density-functional calculations to explore the motivations for cation diffusion. We find that superionic behavior in Li 2B 12H 12 and Na 2B 12H 12 results from a combination of key structural, chemical, and dynamical factors that introduce intrinsicmore » frustration and disorder. A statistical metric is used to show that the structures exhibit a high density of accessible interstitial sites and site types, which correlates with the flatness of the energy landscape and the observed cation mobility. Furthermore, cations are found to dock to specific anion sites, leading to a competition between the geometric symmetry of the anion and the symmetry of the lattice itself, which can facilitate cation hopping. Finally, facile anion reorientations and other low-frequency thermal vibrations lead to fluctuations in the local potential that enhance cation mobility by creating a local driving force for hopping. In conclusion, we discuss the relevance of each factor for developing new ionic conductivity descriptors that can be used for discovery and optimization of closo-borate solid electrolytes, as well as superionic conductors more generally.« less

Insights into gelation kinetics and gel front migration in cation-induced polysaccharide hydrogels by viscoelastic and turbidity measurements: Effect of the nature of divalent cations.

PubMed

Huynh, Uyen T D; Chambin, Odile; du Poset, Aline Maire; Assifaoui, Ali

2018-06-15

Polysaccharide-based hydrogels were prepared by the diffusion of various divalent cations (X 2+ ) into the polygalacturonate (polyGal) solution through a dialysis membrane. The diffusion of various divalent cations (Mg 2+ , Ca 2+ , Zn 2+ and Ba 2+ ) was investigated. The polyGal gel growth was studied as a function of the initial cation concentration by both viscoelastic and turbidity measurements. We have demonstrated for the first time that the determination of the spatiotemporal variation of turbidity during the gelation process allowed to study the gel front migration. For Ca-polyGal, Zn-polyGal and Ba-polyGal, the gel front migration was characterized by the presence of a peak at the sol/gel interface. This peak was not observed in the case of Mg-polyGal where the gel was not formed. The apparent diffusion coefficient of the gel front (D app ) which was calculated from the evolution of this peak increased when the initial cation concentration was increased. Moreover, we have suggested a gelation mechanism based on the presence of a threshold molar ratio R* (=[X 2+ ]/[Galacturonic unit]) in which some point-like crosslinks are precursors of the formation of dimers and multimers inducing the contraction of the gel and thus the formation of the gel front. Copyright © 2018 Elsevier Ltd. All rights reserved.

Structural vs. intrinsic carriers: contrasting effects of cation chemistry and disorder on ionic conductivity in pyrochlores

DOE PAGES

Perriot, Romain; Uberuaga, Blas P.

2015-04-21

We use molecular dynamics simulations to investigate the role of cation disorder on oxygen diffusion in Gd 2Zr 2O 7 (GZO) and Gd 2Ti 2O 7 (GTO) pyrochlores, a class of complex oxides which contain a structural vacancy relative to the basic fluorite structure. The introduction of disorder has distinct effects depending on the chemistry of the material, increasing the mobility of structural carriers by up to four orders of magnitude in GZO. In contrast, in GTO, there is no mobility at zero or low disorder on the ns timescale, but higher disorder liberates the otherwise immobile carriers, allowing diffusionmore » with rates comparable to GZO for the fully disordered material. Here, we show that the cation disorder enhances the diffusivity by both increasing the concentration of mobile structural carriers and their individual mobility. The disorder also influences the diffusion in materials containing intrinsic carriers, such as additional vacancies VO or oxygen interstitials OI. And while in ordered GZO and GTO the contribution of the intrinsic carriers dominates the overall diffusion of oxygen, OI in GZO contributes along with structural carriers, and the total diffusion rate can be calculated by assuming simple additive contributions from the two sources. Although the disorder in the materials with intrinsic defects usually enhances the diffusivity as in the defect-free case, in low concentrations, cation antisites AB or BA, where A = Gd and B = Zr or Ti, can act as traps for fast intrinsic defects. The trapping results in a lowering of the diffusivity, and causes a non-monotonic behavior of the diffusivity with disorder. Conversely, in the case of slow intrinsic defects, the main effect of the disorder is to liberate the structural carriers, resulting in an increase of the diffusivity regardless of the defect trapping.« less

Cationic Contrast Agent Diffusion Differs Between Cartilage and Meniscus.

PubMed

Honkanen, Juuso T J; Turunen, Mikael J; Freedman, Jonathan D; Saarakkala, Simo; Grinstaff, Mark W; Ylärinne, Janne H; Jurvelin, Jukka S; Töyräs, Juha

2016-10-01

Contrast enhanced computed tomography (CECT) is a non-destructive imaging technique used for the assessment of composition and structure of articular cartilage and meniscus. Due to structural and compositional differences between these tissues, diffusion and distribution of contrast agents may differ in cartilage and meniscus. The aim of this study is to determine the diffusion kinematics of a novel iodine based cationic contrast agent (CA(2+)) in cartilage and meniscus. Cylindrical cartilage and meniscus samples (d = 6 mm, h ≈ 2 mm) were harvested from healthy bovine knee joints (n = 10), immersed in isotonic cationic contrast agent (20 mgI/mL), and imaged using a micro-CT scanner at 26 time points up to 48 h. Subsequently, normalized X-ray attenuation and contrast agent diffusion flux, as well as water, collagen and proteoglycan (PG) contents in the tissues were determined. The contrast agent distributions within cartilage and meniscus were different. In addition, the normalized attenuation and diffusion flux were higher (p < 0.05) in cartilage. Based on these results, diffusion kinematics vary between cartilage and meniscus. These tissue specific variations can affect the interpretation of CECT images and should be considered when cartilage and meniscus are assessed simultaneously.

A comparative study on the effect of Curcumin and Chlorin-p6 on the diffusion of two organic cations across a negatively charged lipid bilayer probed by second harmonic spectroscopy

NASA Astrophysics Data System (ADS)

Saini, R. K.; Varshney, G. K.; Dube, A.; Gupta, P. K.; Das, K.

2014-09-01

The influence of Curcumin and Chlorin-p6 (Cp6) on the real time diffusion kinetics of two organic cations, LDS (LDS-698) and Malachite Green (MG) across a negatively charged phospholipid bilayer is investigated by Second Harmonic (SH) spectroscopy. The diffusion time constant of LDS at neutral pH in liposomes containing either Curcumin or Cp6 is significantly reduced, the effect being more pronounced with Curcumin. At acidic pH, the quantum of reduction in the diffusion time constant of MG by both the drugs was observed to be similar. The relative changes in the average diffusion time constants of the cations with increasing drug concentration at pH 5.0 and 7.4 shows a substantial pH effect for Curcumin induced membrane permeability, while a modest pH effect was observed for Cp6 induced membrane permeability. Based on available evidence this can be attributed to the increased interaction between the drug and the polar head groups of the lipid at pH 7.4 where the drug resides closer to the lipid-water interface.

Effect of cation ordering on oxygen vacancy diffusion pathways in double perovskites

DOE PAGES

Uberuaga, Blas Pedro; Pilania, Ghanshyam

2015-07-08

Perovskite structured oxides (ABO 3) are attractive for a number of technological applications, including as superionics because of the high oxygen conductivities they exhibit. Double perovskites (AA’BB’O 6) provide even more flexibility for tailoring properties. Using accelerated molecular dynamics, we examine the role of cation ordering on oxygen vacancy mobility in one model double perovskite SrLaTiAlO 6. We find that the mobility of the vacancy is very sensitive to the cation ordering, with a migration energy that varies from 0.6 to 2.7 eV. In the extreme cases, the mobility is both higher and lower than either of the two endmore » member single perovskites. Further, the nature of oxygen vacancy diffusion, whether one-dimensional, two-dimensional, or three-dimensional, also varies with cation ordering. We correlate the dependence of oxygen mobility on cation structure to the distribution of Ti 4+ cations, which provide unfavorable environments for the positively charged oxygen vacancy. The results demonstrate the potential of using tailored double perovskite structures to precisely control the behavior of oxygen vacancies in these materials.« less

Fast kinetics of magnesium monochloride cations in interlayer-expanded titanium disulfide for magnesium rechargeable batteries

DOE PAGES

Yoo, Hyun Deog; Liang, Yanliang; Dong, Hui; ...

2017-08-24

Magnesium rechargeable batteries potentially offer high-energy density, safety, and low cost due to the ability to employ divalent, dendrite-free, and earth-abundant magnesium metal anode. Despite recent progress, further development remains stagnated mainly due to the sluggish scission of magnesium-chloride bond and slow diffusion of divalent magnesium cations in cathodes. Here in this paper we report a battery chemistry that utilizes magnesium monochloride cations in expanded titanium disulfide. Combined theoretical modeling, spectroscopic analysis, and electrochemical study reveal fast diffusion kinetics of magnesium monochloride cations without scission of magnesium-chloride bond. The battery demonstrates the reversible intercalation of 1 and 1.7 magnesium monochloridemore » cations per titanium at 25 and 60 °C, respectively, corresponding to up to 400 mAh g -1 capacity based on the mass of titanium disulfide. The large capacity accompanies with excellent rate and cycling performances even at room temperature, opening up possibilities for a variety of effective intercalation hosts for multivalent-ion batteries.« less

Cation dynamics in the pyridinium based ionic liquid 1-N-butylpyridinium bis((trifluoromethyl)sulfonyl) as seen by quasielastic neutron scattering.

PubMed

Embs, Jan P; Burankova, Tatsiana; Reichert, Elena; Hempelmann, Rolf

2012-11-08

Quasielastic neutron scattering (QENS) has been used to study the cation dynamics in the pyridinium based ionic liquid (IL) 1-N-butylpyridinium bis((trifluoromethyl)sulfonyl)imide (BuPy-Tf(2)N). This IL allows for a detailed investigation of the dynamics of the cations only, due to the huge incoherent scattering cross section of the cation (σ(inc)(cation) > σ(inc)(anion)). The measured spectra can be decomposed into two Lorentzian lines, indicative of two distinct dynamic processes. The slower of these two processes is diffusive in nature, whereas the faster one can be attributed to localized motions. The temperature dependence of the diffusion coefficient of the slow process follows an Arrhenius law, with an activation energy of E(A) = 14.8 ± 0.3 kJ/mol. Furthermore, we present here results from experiments with polarized neutrons. These experiments clearly show that the slower of the two observed processes is coherent, while the faster one is incoherent in nature.

Diffusion, sorption, and retardation processes of anions in bentonite and organo-bentonites for multibarrier systems

NASA Astrophysics Data System (ADS)

Schampera, Birgit; Dultz, Stefan

2013-04-01

The low permeability, high cation exchange capacity (CEC) and plasticity of bentonites favor their use in multibarrier systems of waste deposits [1]. Bentonites have a high CEC but their ability to sorb anions is very low. There is, however, need for retardation of anions and organic pollutants in many applications. Bentonites, modified with certain organic cations, have the capacity to sorb anions and non-polar organic compounds in addition to cations. Investigations on organically modified clays address a wide variety of applications including immobilization of pollutants in contaminated soils, waste water treatment and in situ placement for the protection of ground water [2]. Many experiments on anion and cation sorption of organo-clays were conducted in the batch mode which does not reflect solid-liquid ratios and material densities in barrier systems. Diffusion experiments on compacted clays allow the evaluation of transport processes and sorption of pollutants at conditions relevant for repositories. For organo-clays only few diffusion studies are published e.g. [3] measured the diffusion of tritium and [4] the diffusion of H2O in bentonite and organo-bentonites. The organic cation hexadecylpyridinium (HDPy) was added to Wyoming bentonite (MX-80) in amounts corresponding to 2-400 % of the CEC. The uptake of organic cations was determined by the C-content, XRD and IR-spectroscopy. Wettability was analyzed by the contact angle. Physical, chemical and mineralogical properties of clays were characterized. Diffusion experiments were carried out in situ in a cell attached to the ATR-unit of a FTIR-spectrometer. For H2O-diffusion the compacted organo-clays are saturated first with D2O, afterwards H2O is supplied to the surface at the top of the clay platelet. Anion-diffusion was conducted with NO3--solution instead of H2O only having characteristic IR band positions at 1350 cm-1. Three different concentrations (0.25M, 0.5M and 1M) were used. Additional batch experiments with NO3- will support the understanding of sorption behavior of the anions. All hydrophilic samples have a higher retardation capacity, indicated by diffusion coefficients of 2.44 x 10-11 m/s2 for original bentonite and ˜2.1 x 10-11m/s2 for hydrophilic organo-clays. For hydrophobic organo-clays the H2O diffusion can be higher and is increased at high bulk density (1-1.5 g/m3) up to 2.76 x 10-10m2/s. Experiments with NO3- at bulk density of 1.5 g/m3 reveal that the apparent diffusion coefficients of nitrate are with results up to 5.61 x 1012 m2/s distinctively lower than free diffusion of nitrate in pure water (6.46 x 1010 m2/s at experimental conditions) and nitrate diffusion in natural bentonite (2.63 x 1011 m2/s). The measurements allow the interpretation of the different sorption mechanisms, retardation capacity and diffusion behavior of the analyzed clays at different anion concentrations. Ongoing molecular dynamic simulations will contribute understanding of diffusion processes in organo-clays including the conditions at the interface of the clay minerals and in solution. References: [1] Shackelford, C.D., Moore S.M. (2013) Fickian diffusion of radionuclides for engineered containment barriers: Diffusion coefficients, porosities, and complicating issues. Engineering Geology, 152, 133-147. [2] Rytwo, G., Nir, S., Shuali, U. (2012) Clay and water treatment. Applied Clay Science, 67-68, 117-118. [3] Lorenzetti, R.L., Bartelt-Hunt, S.L., Burns, S.E., Smith, J.A. (2005) Hydraulic conductivities and effective diffusion coefficients of geosynthetic clay liners with organobentonite amendments. Geotextiles and Geomembranes, 23, 385-400. [4] Schampera, B., Dultz, S. (2011) H2O self-diffusion in compacted clays as influenced by surface charge and wettability - obstruction effects of bound H2O layers. Clay and Clay Minerals,59, 42-57.

Effects of cation contaminants in conductive TiO2 ceramics

NASA Astrophysics Data System (ADS)

Yan, M. F.; Rhodes, W. W.

1982-12-01

Ten cation contaminants, namely Al, Ga, Co, Fe, Mg, Zn, Zr, Ca, Sr, and Ba were investigated for their effects on the electrical properties, microstructures, and discoloration of conductive TiO2 ceramics. It was found that Al, Ga, Co, Fe, and Mg cause discoloration and increase the electrical resistivity by a factor of 104 to 106 in Nb-doped TiO2 ceramics. The other dopants do not introduce such changes in TiO2. The electrical properties, microstructures, and discoloration were measured in specimens of AlxNb0.007Ti0.993-xO2 with 0≤x≤0.01. When the Al content exceeds a critical value, ranging from 0.48% at 1400 °C to 0.25% at 1200 °C, the electrical resistivities and grain size increase rapidly, and the specimen is discolored from the original black to an ivory white color. Color boundary migration induced by Al diffusion in Nb-doped TiO2 was quantitatively measured. From the kinetics of the boundary migration, the Al diffusivity (D) was calculated to be D=2.67 exp(-53.3 kcal/mole/RT) cm2/s in the temperature range of 1200 to 1400 °C. The rapid diffusion of the small cations, namely Al, Ga, Co, Fe, and Mg, results from an interstitial diffusion mechanism. However, other cations, having a radius larger than the interstitial channel (˜0.77 Å radius), cannot diffuse by this mechanism. Defect reactions are proposed to explain the increase in the electrical resistivity and microstructural changes due to Al diffusion. These defect reactions also show that the problem of acceptor contamination cannot be avoided by adding an excess quantity of donor dopant if the solubility of the donor is much less than that of the acceptor contaminant.

Time Dependent Density Functional Theory Calculations of Large Compact PAH Cations: Implications for the Diffuse Interstellar Bands

NASA Technical Reports Server (NTRS)

Weisman, Jennifer L.; Lee, Timothy J.; Salama, Farid; Gordon-Head, Martin; Kwak, Dochan (Technical Monitor)

2002-01-01

We investigate the electronic absorption spectra of several maximally pericondensed polycyclic aromatic hydrocarbon radical cations with time dependent density functional theory calculations. We find interesting trends in the vertical excitation energies and oscillator strengths for this series containing pyrene through circumcoronene, the largest species containing more than 50 carbon atoms. We discuss the implications of these new results for the size and structure distribution of the diffuse interstellar band carriers.

Visual tracing of diffusion and biodistribution for amphiphilic cationic nanoparticles using photoacoustic imaging after ex vivo intravitreal injections

PubMed Central

Xu, Xu; Xu, Zhaokang; Liu, Junyi; Zhang, Zhaoliang; Chen, Hao; Li, Xingyi; Shi, Shuai

2016-01-01

To visually trace the diffusion and biodistribution of amphiphilic cation micelles after vitreous injection, various triblock copolymers of monomethoxy poly(ethylene glycol)–poly(ε-caprolactone)–polyethylenimine were synthesized with different structures of hydrophilic and hydrophobic segments, followed by labeling with near-infrared fluorescent dye Cyanine5 or Cyanine7. The micellar size, polydispersity index, and surface charge were measured by dynamic light scattering. The diffusion was monitored using photoacoustic imaging in real time after intravitreal injections. Moreover, the labeled nanoparticle distribution in the posterior segment of the eye was imaged histologically by confocal microscopy. The results showed that the hydrophilic segment increased vitreous diffusion, while a positive charge on the particle surface hindered diffusion. In addition, the particles diffused through the retinal layers and were enriched in the retinal pigment epithelial layer. This work tried to study the diffusion rate via a simple method by using visible images, and then provided basic data for the development of intraocular drug carriers. PMID:27785015

Visual tracing of diffusion and biodistribution for amphiphilic cationic nanoparticles using photoacoustic imaging after ex vivo intravitreal injections.

PubMed

Xu, Xu; Xu, Zhaokang; Liu, Junyi; Zhang, Zhaoliang; Chen, Hao; Li, Xingyi; Shi, Shuai

To visually trace the diffusion and biodistribution of amphiphilic cation micelles after vitreous injection, various triblock copolymers of monomethoxy poly(ethylene glycol)-poly(ε-caprolactone)-polyethylenimine were synthesized with different structures of hydrophilic and hydrophobic segments, followed by labeling with near-infrared fluorescent dye Cyanine5 or Cyanine7. The micellar size, polydispersity index, and surface charge were measured by dynamic light scattering. The diffusion was monitored using photoacoustic imaging in real time after intravitreal injections. Moreover, the labeled nanoparticle distribution in the posterior segment of the eye was imaged histologically by confocal microscopy. The results showed that the hydrophilic segment increased vitreous diffusion, while a positive charge on the particle surface hindered diffusion. In addition, the particles diffused through the retinal layers and were enriched in the retinal pigment epithelial layer. This work tried to study the diffusion rate via a simple method by using visible images, and then provided basic data for the development of intraocular drug carriers.

Functional analysis of two genes coding for distinct cation diffusion facilitators of the ectomycorrhizal Zn-accumulating fungus Russula atropurpurea.

PubMed

Sácký, Jan; Leonhardt, Tereza; Kotrba, Pavel

2016-04-01

Russula atropurpurea can accumulate remarkably high concentrations of Zn in its sporocarps. We have previously demonstrated that 40 % of the intracellular Zn in this species is sequestered by MT-like RaZBP peptides. To see what other mechanisms for the handling of the accumulated Zn are available to R. atropurpurea, we searched its transcriptome for cDNAs coding for transporters of the cation diffusion facilitator (CDF) family. The transcriptome search enabled us to identify RaCDF1 and RaCDF2, which were further subjected to functional studies in metal sensitive Saccharomyces cerevisiae. The expression of RaCDF1 and its translational fusion with green fluorescent protein (GFP) protected the yeasts against Zn and Co, but not Cd or Mn, toxicity and led to increased Zn accumulation in the cells. The GFP fluorescence, observed in the RaCDF1::GFP-expressing yeasts on tonoplasts, indicated that the RaCDF1-mediated Zn and Co tolerance was a result of vacuolar sequestration of the metals. The expression of RaCDF2 supported Zn, but not Mn, tolerance in the yeasts and reduced the cellular uptake of Zn, which is congruent with the proposed idea of the Zn-efflux function of RaCDF2, supported by the localization of GFP-derived fluorescence on the plasma membrane of the yeasts expressing functional RaCDF2::GFP. Contrarily, RaCDF2 increased the sensitivity to Co and Cd in the yeasts and significantly promoted Cd uptake, which suggested that it can act as a bidirectional metal transporter. The notion that RaCDF1 and RaCDF2 are genuine CDF transporters in R. atropurputrea was further reinforced by the fact that the RaCDF-associated metal tolerance and uptake phenotypes were lost upon the replacement of histidyl (in RaCDF1) and aspartyl (in RaCDF2), which are highly conserved in the second transmembrane domain and known to be essential for the function of CDF proteins.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoo, Hyun Deog; Liang, Yanliang; Dong, Hui

Magnesium rechargeable batteries potentially offer high-energy density, safety, and low cost due to the ability to employ divalent, dendrite-free, and earth-abundant magnesium metal anode. Despite recent progress, further development remains stagnated mainly due to the sluggish scission of magnesium-chloride bond and slow diffusion of divalent magnesium cations in cathodes. Here in this paper we report a battery chemistry that utilizes magnesium monochloride cations in expanded titanium disulfide. Combined theoretical modeling, spectroscopic analysis, and electrochemical study reveal fast diffusion kinetics of magnesium monochloride cations without scission of magnesium-chloride bond. The battery demonstrates the reversible intercalation of 1 and 1.7 magnesium monochloridemore » cations per titanium at 25 and 60 °C, respectively, corresponding to up to 400 mAh g -1 capacity based on the mass of titanium disulfide. The large capacity accompanies with excellent rate and cycling performances even at room temperature, opening up possibilities for a variety of effective intercalation hosts for multivalent-ion batteries.« less

Experimental characterization and modelization of ion exchange kinetics for a carboxylic resin in infinite solution volume conditions. Application to monovalent-trivalent cations exchange.

PubMed

Picart, Sébastien; Ramière, Isabelle; Mokhtari, Hamid; Jobelin, Isabelle

2010-09-02

This study is devoted to the characterization of ion exchange inside a microsphere of carboxylic resin. It aims at describing the kinetics of this exchange reaction which is known to be controlled by interdiffusion in the particle. The fractional attainment of equilibrium function of time depends on the concentration of the cations in the resin which can be modelized by the Nernst-Planck equation. A powerful approach for the numerical resolution of this equation is introduced in this paper. This modeling is based on the work of Helfferich but involves an implicit numerical scheme which reduces the computational cost. Knowing the diffusion coefficients of the cations in the resin and the radius of the spherical exchanger, the kinetics can be hence completely determined. When those diffusion parameters are missing, they can be deduced by fitting experimental data of fractional attainment of equilibrium. An efficient optimization tool coupled with the implicit resolution has been developed for this purpose. A monovalent/trivalent cation exchange had been experimentally characterized for a carboxylic resin. Diffusion coefficients and concentration profiles in the resin were then deduced through this new model.

Electronic spectra of astrophysically interesting cations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maier, John P., E-mail: j.p.maier@unibas.ch; Rice, Corey A., E-mail: j.p.maier@unibas.ch; Mazzotti, Fabio J., E-mail: j.p.maier@unibas.ch

2015-01-22

The electronic spectra of polyacetylene cations were recorded at 20K in the laboratory in an ion trap instrument. These can then be compared with diffuse interstellar band (DIB) absorptions. Examination of recently published data shows that the attribution of a weak DIB at ∼506.9 nm to diacetylene cation is not justified. Study of the higher excited electronic states of polyacetylene cations shows that their widths can still be sufficiently narrow for consideration as DIB carriers.

Quasielastic neutron scattering studies on glass-forming ionic liquids with imidazolium cations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kofu, Maiko; Inamura, Yasuhiro; Miyazaki, Kyoko

2015-12-21

Relaxation processes for imidazolium-based ionic liquids (ILs) were investigated by means of an incoherent quasielastic neutron scattering technique. In order to clarify the cation and anion effects on the relaxation processes, ten samples were measured. For all of the samples, we found three relaxations at around 1 ps, 10 ps, and 100 ps-10 ns, each corresponding to the alkyl reorientation, the relaxation related to the imidazolium ring, and the ionic diffusion. The activation energy (E{sub a}) for the alkyl relaxation is insensitive to both anion and alkyl chain lengths. On the other hand, for the imidazolium relaxation and the ionicmore » diffusion processes, E{sub a} increases as the anion size decreases but is almost independent of the alkyl chain length. This indicates that the ionic diffusion and imidazolium relaxation are governed by the Coulombic interaction between the core parts of the cations (imidazolium ring) and the anions. This is consistent with the fact that the imidazolium-based ILs have nanometer scale structures consisting of ionic and neutral (alkyl chain) domains. It is also found that there is a clear correlation between the ionic diffusion and viscosity, indicating that the ionic diffusion is mainly associated with the glass transition which is one of the characteristics of imidazolium-based ILs.« less

Nuclear magnetic resonance investigation of dynamics in poly(ethylene oxide) based polyether-ester-sulfonate ionomers

NASA Astrophysics Data System (ADS)

Roach, David J.

Nuclear magnetic resonance (NMR) spectroscopy has been utilized to investigate the dynamics of poly(ethylene oxide)-based lithium sulfonate ionomer samples that have low glass transition temperatures. 1H and 7Li spin-lattice relaxation times (T1) of the bulk polymer and lithium ions, respectively, were measured and analyzed in samples with a range of ion contents. The temperature dependence of T1 values along with the presence of minima in T1 as a function of temperature enabled correlation times and activation energies to be obtained for both the segmental motion of the polymer backbone and the hopping motion of lithium cations. Similar activation energies for motion of both the polymer and lithium ions in the samples with lower ion content indicate that the polymer segmental motion and lithium ion hopping motion are correlated in these samples, even though lithium hopping is about ten times slower than the segmental motion. A divergent trend is observed for correlation times and activation energies of the highest ion content sample with 100% lithium sulfonation due to the presence of ionic aggregation. Details of the polymer and cation dynamics on the nanosecond timescale are discussed and complement the findings of X-ray scattering and Quasi Elastic Neutron Scattering experiments. Polymer backbone dynamics of single ion conducting poly(ethylene oxide) (PEO)-based ionomer samples with low glass transition temperatures (T g) have been investigated using solid-state nuclear magnetic resonance (NMR). Experiments detecting 13C with 1H decoupling under magic angle spinning (MAS) conditions identified the different components and relative mobilities of the polymer backbone of a suite of. lithium- and sodium-containing ionomer samples with varying cation contents. Variable temperature (203-373 K) 1H-13C cross-polarization MAS (CP-MAS) experiments also provided qualitative assessment of the differences in the motions of the polymer backbone components as a function of cation content. Each of the main backbone components (PEO spacer and isophthalate groups) exhibit distinct motions, following the trends expected for motional characteristics based on earlier Quasi Elastic Neutron Scattering and 1H spin-lattice relaxation rate measurements. The temperature dependences of 13C linewidths were used to both qualitatively and quantitatively examine the effects of cation content on PEO mobility. Variable contact time 1H-13C CP-MAS experiments were used to further assess the motions of the polymer backbone on the microsecond timescale. The motion of the PEO spacer, determined from the rate of magnetization transfer from 1H to 13C nuclei, in all ionic samples becomes similar for T [special characters omitted] 1.1 Tg, indicating that the motions of the polymer backbones on the microsecond timescale become insensitive to ion interactions. These results compliment previous findings and present an improved picture of the dependence of backbone dynamics on cation type and density in these amorphous PEO-based ionomer systems. 7Li PFG NMR experiments provided measurements of the self-diffusion coefficients for Li+ cations in the PEO600-y Li ionomer series over a range of temperatures. When the Tg values are taken into account, the self-diffusion coefficients of Li+ in each sample follow a similar trendline, indicating that lithium diffusion is independent of ion concentration at any given reduced inverse temperature, Tg/T. Ion aggregation increases Tg and slows both lithium cation diffusion and displacement, but there is no further slowing beyond the Tg effect in the PEO600-y Li ionomers samples. The differences in activation energies obtained from diffusion measurements and relaxation times suggest that at least one additional barrier must be overcome for cations emerge from local hopping motion to macroscopic cation transpfort. Using the Nernst- Einstein equation lithium diffusion coefficients were also calculated from conductivity measurements. The differences between the diffusion measured by the two separate techniques indicate the presence of ion pairs. The activation energy of lithium diffusion was found to be nearly identical between the PFG NMR and conductivity, suggesting that the conductivity and ionic diffusion are related to the same ionic dynamics. As the ion content within the PEO600-y Li samples increases the relative concentration of nonconducting ion pairs decrease. Also an increase in temperature causes a fraction of ion pairs to thermally dissociate into positive triple ions.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perriot, Romain; Uberuaga, Blas P.

We use molecular dynamics simulations to investigate the role of cation disorder on oxygen diffusion in Gd 2Zr 2O 7 (GZO) and Gd 2Ti 2O 7 (GTO) pyrochlores, a class of complex oxides which contain a structural vacancy relative to the basic fluorite structure. The introduction of disorder has distinct effects depending on the chemistry of the material, increasing the mobility of structural carriers by up to four orders of magnitude in GZO. In contrast, in GTO, there is no mobility at zero or low disorder on the ns timescale, but higher disorder liberates the otherwise immobile carriers, allowing diffusionmore » with rates comparable to GZO for the fully disordered material. Here, we show that the cation disorder enhances the diffusivity by both increasing the concentration of mobile structural carriers and their individual mobility. The disorder also influences the diffusion in materials containing intrinsic carriers, such as additional vacancies VO or oxygen interstitials OI. And while in ordered GZO and GTO the contribution of the intrinsic carriers dominates the overall diffusion of oxygen, OI in GZO contributes along with structural carriers, and the total diffusion rate can be calculated by assuming simple additive contributions from the two sources. Although the disorder in the materials with intrinsic defects usually enhances the diffusivity as in the defect-free case, in low concentrations, cation antisites AB or BA, where A = Gd and B = Zr or Ti, can act as traps for fast intrinsic defects. The trapping results in a lowering of the diffusivity, and causes a non-monotonic behavior of the diffusivity with disorder. Conversely, in the case of slow intrinsic defects, the main effect of the disorder is to liberate the structural carriers, resulting in an increase of the diffusivity regardless of the defect trapping.« less

How ion properties determine the stability of a lipase enzyme in ionic liquids: a molecular dynamics study.

PubMed

Klähn, Marco; Lim, Geraldine S; Wu, Ping

2011-11-07

The influence of eight different ionic liquid (IL) solvents on the stability of the lipase Candida antarctica lipase B (CAL-B) is investigated with molecular dynamics (MD) simulations. Considered ILs contain cations that are based either on imidazolium or guanidinium as well as nitrate, tetrafluoroborate or hexafluorophosphate anions. Partial unfolding of CAL-B is observed during high-temperature MD simulations and related changes of CAL-B regarding its radius of gyration, surface area, secondary structure, amount of solvent close to the backbone and interaction strength with the ILs are evaluated. CAL-B stability is influenced primarily by anions in the order NO(3)(-)≪ BF(4)(-) < PF(6)(-) of increasing stability, which agrees with experiments. Cations influence protein stability less than anions but still substantially. Long decyl side chains, polar methoxy groups and guanidinium-based cations destabilize CAL-B more than short methyl groups, other non-polar groups and imidazolium-based cations, respectively. Two distinct causes for CAL-B destabilization are identified: a destabilization of the protein surface is facilitated mostly by strong Coulomb interactions of CAL-B with anions that exhibit a localized charge and strong polarization as well as with polar cation groups. Surface instability is characterized by an unraveling of α-helices and an increase of surface area, radius of gyration and protein-IL total interaction strength of CAL-B, all of which describe a destabilization of the folded protein state. On the other hand, a destabilization of the protein core is facilitated when direct core-IL interactions are feasible. This is the case when long alkyl chains are involved or when particularly hydrophobic ILs induce major conformational changes that enable ILs direct access to the protein core. This core instability is characterized by a disintegration of β-sheets, diffusion of ions into CAL-B and increasing protein-IL van der Waals interactions. This process describes a stabilization of the unfolded protein state. Both of these processes reduce the folding free energy and thus destabilize CAL-B. The results of this work clarify the impact of ions on CAL-B stabilization. An extrapolation of the observed trends enables proposing novel ILs in which protein stability could be enhanced further. This journal is © the Owner Societies 2011

Insights into dynamic processes of cations in pyrochlores and other complex oxides

DOE PAGES

Uberuaga, Blas Pedro; Perriot, Romain

2015-08-26

Complex oxides are critical components of many key technologies, from solid oxide fuel cells and superionics to inert matrix fuels and nuclear waste forms. In many cases, understanding mass transport is important for predicting performance and, thus, extensive effort has been devoted to understanding mass transport in these materials. However, most work has focused on the behavior of oxygen while cation transport has received relatively little attention, even though cation diffusion is responsible for many phenomena, including sintering, radiation damage evolution, and deformation processes. Here, we use accelerated molecular dynamics simulations to examine the kinetics of cation defects in onemore » class of complex oxides, A₂B₂O₇ pyrochlore. In some pyrochlore chemistries, B cation defects are kinetically unstable, transforming to A cation defects and antisites at rates faster than they can diffuse. When this occurs, transport of B cations occurs through defect processes on the A sublattice. Further, these A cation defects, either interstitials or vacancies, can interact with antisite disorder, reordering the material locally, though this process is much more efficient for interstitials than vacancies. Whether this behavior occurs in a given pyrochlore depends on the A and B chemistry. Pyrochlores with a smaller ratio of cation radii exhibit this complex behavior, while those with larger ratios exhibit direct migration of B interstitials. Similar behavior has been reported in other complex oxides such as spinels and perovskites, suggesting that this coupling of transport between the A and B cation sublattices, while not universal, occurs in many complex oxide.« less

Diffusion of a Highly-Charged Supramolecular Assembly: Direct Observation of Ion-Association in Water

DOE Office of Scientific and Technical Information (OSTI.GOV)

University of California, Berkeley; Lawrence Berkeley National Laboratory; Raymond, Kenneth

2007-10-22

Understanding the solution behavior of supramolecular assemblies is essential for a full understanding of the formation and chemistry of synthetic host-guest systems. While the interaction between host and guest molecules is generally the focus of mechanistic studies of host-guest complexes, the interaction of the host-guest complex with other species in solution remains largely unknown, although in principle accessible by diffusion studies. Several NMR techniques are available to monitor diffusion and have recently been reviewed. Pulsed gradient spin-echo (PGSE) NMR methods have attracted increasing interest, since they allow diffusion coefficients to be measured with high accuracy; they have been successfully usedmore » with observation of {sup 7}Li and {sup 31}P nuclei as well as with {sup 1}H NMR. We report here the direct measurement of diffusion coefficients to observe ion-association interactions by counter cations with a highly-charged supramolecular assembly. Raymond and coworkers have described the design and chemistry of a class of metal-ligand supramolecular assemblies over the past decade. The [Ga{sub 4}L{sub 6}]{sup 12-} (L = 1,5-bis(2,3-dihydroxybenzamido)naphthalene) (1) (Figure 1) assembly has garnered the most attention, with the exploration of the dynamics and mechanism of guest exchange as well as the ability of 1 to achieve either stoichiometric or catalytic reactions inside its interior cavity. Recent studies have revealed the importance of counter cations in solution on the chemistry of 1. During the mechanistic study of the C-H bond activation of aldehydes by [Cp*Ir(PMe{sub 3})(olefin){sup +} {contained_in} 1]{sup 11-} a stepwise guest dissociation mechanism with an ion-paired intermediate was proposed. Similarly, in the mechanism for the hydrolysis of iminium cations generated from the 3-aza Cope rearrangement of enammonium cations in 1, the presence of an exterior ion association was part of the kinetic model. To further substantiate the indirect kinetic evidence for such ion-paired species, we sought to explore the solution behavior of 1 by studying the diffusion of 1 with varying alkali and tetraalkyl ammonium cations. For large molecules in solution, such as synthetic supramolecular assemblies, the diffusion behavior of host and guest molecules can provide valuable information on host-guest interaction. One characteristic feature of a stable host-guest complex is that the host and guest molecules diffuse at the same rate in solution; this has been observed in a number of supramolecular systems. In order to confirm that this system was suitable for study by diffusion NMR spectroscopy, a PGSE-DOSY spectrum was acquired of [NEt{sub 4} {contained_in} 1]{sup 11-} (Figure 2), which shows that the host and guest molecules diffuse at the same rate. Quantitative analysis of the data, from monitoring the integral of host and guest resonances as a function of applied gradient strength, gave identical diffusion coefficients, confirming that the host and guest molecules diffuse together.« less

Facilitated diffusion in chromatin lattices: mechanistic diversity and regulatory potential.

PubMed

Kampmann, Martin

2005-08-01

The interaction between a protein and a specific DNA site is the molecular basis for vital processes in all organisms. Location of the DNA target site by the protein commonly involves facilitated diffusion. Mechanisms of facilitated diffusion vary among proteins; they include one- and two-dimensional sliding along DNA, direct transfer between uncorrelated sites, as well as combinations of these mechanisms. Facilitated diffusion has almost exclusively been studied in vitro. This review discusses facilitated diffusion in the context of the living cell and proposes a theoretical model for facilitated diffusion in chromatin lattices. Chromatin structure differentially affects proteins in different modes of diffusion. The interplay of facilitated diffusion and chromatin structure can determine the rate of protein association with the target site, the frequency of association-dissociation events at the target site, and, under particular conditions, the occupancy of the target site. Facilitated diffusion is required in vivo for efficient DNA repair and bacteriophage restriction and has potential roles in fine-tuning gene regulatory networks and kinetically compartmentalizing the eukaryotic nucleus.

Li Storage of Calcium Niobates for Lithium Ion Batteries.

PubMed

Yim, Haena; Yu, Seung-Ho; Yoo, So Yeon; Sung, Yung-Eun; Choi, Ji-Won

2015-10-01

New types of niobates negative electrode were studied for using in lithium-ion batteries in order to alternate metallic lithium anodes. The potassium intercalated compound KCa2Nb3O10 and proton intercalated compound HCa2Nb3O10 were studied, and the electrochemical results showed a reversible cyclic voltammetry profile with acceptable discharge capacity. The as-prepared KCa2Nb3O10 negative electrode had a low discharge capacity caused by high overpotential, but the reversible intercalation and deintercalation reaction of lithium ions was activated after exchanging H+ ions for intercalated K+ ions. The initial discharge capacity of HCa2Nb3O10 was 54.2 mAh/g with 92.1% of coulombic efficiency, compared with 10.4 mAh/g with 70.2% of coulombic efficiency for KCa2Nb3O10 at 1 C rate. The improved electrochemical performance of the HCa2Nb3O10 was related to the lower bonding energy between proton cation and perovskite layer, which facilitate Li+ ions intercalating into the cation site, unlike potassium cation and perovskite layer. Also, this negative material can be easily exfoliated to Ca2Nb3O10 layer by using cation exchange process. Then, obtained two-dimensional nanosheets layer, which recently expected to be an advanced electrode material because of its flexibility, chemical stable, and thin film fabricable, can allow Li+ ions to diffuse between the each perovskite layer. Therefore, this new type layered perovskite niobates can be used not only bulk-type lithium ion batteries but also thin film batteries as a negative material.

Transformers: the changing phases of low-dimensional vanadium oxide bronzes.

PubMed

Marley, Peter M; Horrocks, Gregory A; Pelcher, Kate E; Banerjee, Sarbajit

2015-03-28

In this feature article, we explore the electronic and structural phase transformations of ternary vanadium oxides with the composition MxV2O5 where M is an intercalated cation. The periodic arrays of intercalated cations ordered along quasi-1D tunnels or layered between 2D sheets of the V2O5 framework induce partial reduction of the framework vanadium atoms giving rise to charge ordering patterns that are specific to the metal M and stoichiometry x. This periodic charge ordering makes these materials remarkably versatile platforms for studying electron correlation and underpins the manifestation of phenomena such as colossal metal-insulator transitions, quantized charge corrals, and superconductivity. We describe current mechanistic understanding of these emergent phenomena with a particular emphasis on the benefits derived from scaling these materials to nanostructured dimensions wherein precise ordering of cations can be obtained and phase relationships can be derived that are entirely inaccessible in the bulk. In particular, structural transformations induced by intercalation are dramatically accelerated due to the shorter diffusion path lengths at nanometer-sized dimensions, which cause a dramatic reduction of kinetic barriers to phase transformations and facilitate interconversion between the different frameworks. We conclude by summarizing numerous technological applications that have become feasible due to recent advances in controlling the structural chemistry and both electronic and structural phase transitions in these versatile frameworks.

Molecular dynamic simulation of dicationic ionic liquids: effects of anions and alkyl chain length on liquid structure and diffusion.

PubMed

Yeganegi, Saeid; Soltanabadi, Azim; Farmanzadeh, Davood

2012-09-20

Structures and dynamics of nine geminal dicationic ionic liquids (DILs) Cn(mim)2X2, where n = 3, 6, and 9 and X = PF6(-), BF4(-), and Br(-), were studied by molecular dynamic simulations (J. Phys. Chem.B2004, 108, 2038-2047). A force field with a minor modification for C3(mim)2 × 2 was adopted for the simulations. Densities, detailed microscopic structures, mean-square displacements (MSD), and self-diffusivities for various ion pairs from MD simulations have been presented. The calculated densities for C9(mim)2X2 (X = Br(-) and BF4(-)) agreed well with the experimental values. The calculated RDFs show that anions are well organized around the imidazolium rings. The calculated RDFs indicate that, unlike the mono cationic ILs, the anions and cations in DILs distribute homogeneously. Enthalpies of vaporization were calculated and correlated with the structural features of DILs. The local structure of C9(mim)2X2 (X = Br, PF6) was examined by the spatial distribution function (SDF). The calculated SDFs show that similar trends were found by other groups for mono cationic ionic liquids (ILs). The highest probability densities are located around the imidazolium ring hydrogens. The calculated diffusion coefficients show that the ion diffusivities are 1 order of magnitude smaller than that of the mono cationic ionic liquids. The effects of alkyl chain length and anion type on the diffusion coefficient were also studied. The dynamics of the imidazolium rings and the alkyl chain in different time scales have also discussed. The calculated transference numbers show that the anions have the major role in carrying the electric current in a DIL.

Extraordinary effects of specific monovalent cations on activation of reovirus transcriptase by chymotrypsin in vitro.

PubMed

Borsa, J; Sargent, M D; Long, D G; Chapman, J D

1973-02-01

Activation of reovirus transcriptase activity, latent in intact virions, by digestion of purified virions with chymotrypsin (CHT) in vitro shows a stringent requirement for specific monovalent cations. Cs(+), Rb(+), or K(+) ions are capable of facilitating activation by chymotryptic digestion. Na(+), Li(+), or NH(4) (+) ions are not capable of facilitating the CHT activation of polymerase activity and are antagonistic towards the effects of the facilitating ions. The data indicate that the effect of the cations is exerted on activation of the polymerase activity by CHT as opposed to an effect on polymerization per se. This effect may be important biologically in that it provides a mechanism whereby the virion can sense whether it is in an intracellular or an extracellular environment and thereby can avoid premature uncoating.

Disorder-induced transition from grain boundary to bulk dominated ionic diffusion in pyrochlores

DOE PAGES

Perriot, Romain; Dholabhai, Pratik P.; Uberuaga, Blas P.

2017-05-04

In this paper, we use molecular dynamics simulations to investigate the role of grain boundaries (GBs) on ionic diffusion in pyrochlores, as a function of the GB type, chemistry of the compound, and level of cation disorder. We observe that the presence of GBs promotes oxygen transport in ordered and low-disordered systems, as the GBs are found to have a higher concentration of mobile carriers with higher mobilities than in the bulk. Thus, in ordered samples, the ionic diffusion is 2D, localized along the grain boundary. When cation disorder is introduced, bulk carriers begin to contribute to the overall diffusion,more » while the GB contribution is only slightly enhanced. In highly disordered samples, the diffusive behavior at the GBs is bulk-like, and the two contributions (bulk vs. GB) can no longer be distinguished. There is thus a transition from 2D/GB dominated oxygen diffusivity to 3D/bulk dominated diffusivity versus disorder in pyrochlores. Finally, these results provide new insights into the possibility of using internal interfaces to enhance ionic conductivity in nanostructured complex oxides.« less

Connecting the molecular scale to the continuum scale for diffusion processes in smectite-rich porous media.

PubMed

Bourg, Ian C; Sposito, Garrison

2010-03-15

In this paper, we address the manner in which the continuum-scale diffusive properties of smectite-rich porous media arise from their molecular- and pore-scale features. Our starting point is a successful model of the continuum-scale apparent diffusion coefficient for water tracers and cations, which decomposes it as a sum of pore-scale terms describing diffusion in macropore and interlayer "compartments." We then apply molecular dynamics (MD) simulations to determine molecular-scale diffusion coefficients D(interlayer) of water tracers and representative cations (Na(+), Cs(+), Sr(2+)) in Na-smectite interlayers. We find that a remarkably simple expression relates D(interlayer) to the pore-scale parameter δ(nanopore) ≤ 1, a constrictivity factor that accounts for the lower mobility in interlayers as compared to macropores: δ(nanopore) = D(interlayer)/D(0), where D(0) is the diffusion coefficient in bulk liquid water. Using this scaling expression, we can accurately predict the apparent diffusion coefficients of tracers H(2)0, Na(+), Sr(2+), and Cs(+) in compacted Na-smectite-rich materials.

On The Molecular Mechanism Of Positive Novolac Resists

NASA Astrophysics Data System (ADS)

Huang, Jian-Ping; Kwei, T. K.; Reiser, Arnost

1989-08-01

A molecular mechanism for the dissolution of novolac is proposed, based on the idea of a critical degree of deprotonation as being the condition for the transfer of polymer into solution. The rate at which the critical deprotonation condition is achieved is controlled by the supply of developer into a thin penetration zone, and depends in particular on the rate of diffusion of the base cations which are the developer component with the lowest mobility. The penetration zone contains phenolate ions and ion-bound water, but it retains the structure of a rigid polymer membrane, as evidenced by the diffusion coefficient of cations in the pene;tration zone which is several orders of magnitude slower than in an open gel of the same material. When the critical degree of deprotonation is reached, the membrane structure unravels and all subsequent events, chain rearrangement and transfer into solution, occur rapidly. The supralinear dependence of dissolution rate on base concentration and the effect of the size of the base cation are plausibly interpreted by the model. The diffusion of developer components is assumed to occur preferentially via hydrophilic sites in the polymer matrix. These sites define a diffusion path which acts like a hydrophilic diffusion channel. Suitably designed hydrophobic molecules can block some of the channels and in this way alter the dissolution rate. They reduce in effect the diffusion crossect ion of the material. Hydrophilic additives, on the other hand, introduce additional channels into the system and promote dissolution. The concept of diffusion channels appears to provide a unified interpretation for a number of common observations.

Carbon Incorporation and Anion Dynamics as Synergistic Drivers for Ultrafast Diffusion in Superionic LiCB 11H 12 and NaCB 11H 12

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dimitrievska, Mirjana; Shea, Patrick; Kweon, Kyoung E.

The disordered phases ofLiCB 11H 12 and NaCB 11H 12 possess superb superionic conductivities that make them suitable as solid electrolytes. In these materials, cation diffusion correlates with high orientational mobilities of the CB 11H 12 - anions; however, the precise relationship has yet to be demonstrated. In this work, ab initio molecular dynamics and quasielastic neutron scattering are combined to probe anion reorientations and their mechanistic connection to cation mobility over a range of timescales and temperatures. It is found that anions do not rotate freely, but rather transition rapidly between orientations defined by the cation sublattice symmetry. Themore » symmetry-breaking carbon atom in CB 11H 12 - also plays a critical role by perturbing the energy landscape along the instantaneous orientation of the anion dipole, which couples fluctuations in the cation probability density directly to the anion motion. Anion reorientation rates exceed 3 x 10 10 s -1, suggesting the underlying energy landscape fluctuates dynamically on diffusion-relevant timescales. Furthermore, carbon is found to modify the orientational preferences of the anions and aid rotational mobility, creating additional symmetry incompatibilities that inhibit ordering. The results suggest that synergy between the anion reorientational dynamics and the carbon-modified cation-anion interaction accounts for the higher ionic conductivity in CB 11H 12 - salts compared with B 12H 12 2-.« less

Carbon Incorporation and Anion Dynamics as Synergistic Drivers for Ultrafast Diffusion in Superionic LiCB 11H 12 and NaCB 11H 12

DOE PAGES

Dimitrievska, Mirjana; Shea, Patrick; Kweon, Kyoung E.; ...

2018-02-20

The disordered phases ofLiCB 11H 12 and NaCB 11H 12 possess superb superionic conductivities that make them suitable as solid electrolytes. In these materials, cation diffusion correlates with high orientational mobilities of the CB 11H 12 - anions; however, the precise relationship has yet to be demonstrated. In this work, ab initio molecular dynamics and quasielastic neutron scattering are combined to probe anion reorientations and their mechanistic connection to cation mobility over a range of timescales and temperatures. It is found that anions do not rotate freely, but rather transition rapidly between orientations defined by the cation sublattice symmetry. Themore » symmetry-breaking carbon atom in CB 11H 12 - also plays a critical role by perturbing the energy landscape along the instantaneous orientation of the anion dipole, which couples fluctuations in the cation probability density directly to the anion motion. Anion reorientation rates exceed 3 x 10 10 s -1, suggesting the underlying energy landscape fluctuates dynamically on diffusion-relevant timescales. Furthermore, carbon is found to modify the orientational preferences of the anions and aid rotational mobility, creating additional symmetry incompatibilities that inhibit ordering. The results suggest that synergy between the anion reorientational dynamics and the carbon-modified cation-anion interaction accounts for the higher ionic conductivity in CB 11H 12 - salts compared with B 12H 12 2-.« less

First-Principles Analysis of Defect Thermodynamics and Ion Transport in Inorganic SEI Compounds: LiF and NaF

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yildirim, Handan; Kinaci, Alper; Chan, Maria K. Y.

The formation mechanism and composition of the solid electrolyte interphase (SEI) in lithium ion batteries has been widely explored. However, relatively little is known about the function of the SEI as a transport medium. Such critical information is directly relevant to battery rate performance, power loss, and capacity fading. To partially bridge this gap in the case of inorganic SEI compounds, we report herein the results of first-principles calculations on the defect thermodynamics, the dominant diffusion carriers, and the diffusion pathways associated with crystalline LiF and NaF, which are stable components of the SEI in Li-ion and Na-ion batteries, respectively.more » The thermodynamics of common point defects are computed, and the dominant diffusion carriers are determined over a voltage range of 0-4 V, corresponding to conditions relevant to both anode and cathode SEI's. Our analyses reveal that for both compounds, vacancy defects are energetically more favorable, therefore form more readily than interstitials, due to the close-packed nature of the crystal structures. However, the vacancy concentrations are very small for the diffusion processes facilitated by defects. Ionic conductivities are calculated as a function of voltage, considering the diffusion carrier concentration and the diffusion barriers as determined by nudged elastic band calculations. These conductivities are more than ten orders of magnitude smaller in NaF than in LiF. As compared to the diffusivity of Li in other common inorganic SEI compounds, such as Li2CO3 and Li2O,the cation diffusivity in LiF and NaF is quite low, with at least three orders of magnitude lower ionic conductivities. The results quantify the extent to which fluorides pose rate limitations in Li and Na batteries.« less

Effect of cation on diffusion coefficient of ionic liquids at onion-like carbon electrodes.

PubMed

Van Aken, Katherine L; McDonough, John K; Li, Song; Feng, Guang; Chathoth, Suresh M; Mamontov, Eugene; Fulvio, Pasquale F; Cummings, Peter T; Dai, Sheng; Gogotsi, Yury

2014-07-16

While most supercapacitors are limited in their performance by the stability of the electrolyte, using neat ionic liquids (ILs) as the electrolyte can expand the voltage window and temperature range of operation. In this study, ILs with bis(trifluoromethylsulfonyl)imide (Tf2N) as the anion were investigated as the electrolyte in onion-like carbon-based electrochemical capacitors. To probe the influence of cations on the electrochemical performance of supercapacitors, three different cations were used: 1-ethyl-3-methylimidazolium, 1-hexyl-3-methylimidazolium and 1,6-bis(3-methylimidazolium-1-yl). A series of electrochemical characterization tests was performed using cyclic voltammetry (CV), galvanostatic cycling and electrochemical impedance spectroscopy (EIS). Diffusion coefficients were measured using EIS and correlated with quasielastic neutron scattering and molecular dynamics simulation. These three techniques were used in parallel to confirm a consistent trend between the three ILs. It was found that the IL with the smaller sized cation had a larger diffusion coefficient, leading to a higher capacitance at faster charge-discharge rates. Furthermore, the IL electrolyte performance was correlated with increasing temperature, which limited the voltage stability window and led to the formation of a solid electrolyte interphase on the carbon electrode surface, evident in both the CV and EIS experiments.

Effects of sorption competition on caesium diffusion through compacted argillaceous rock

NASA Astrophysics Data System (ADS)

Jakob, Andreas; Pfingsten, Wilfried; Van Loon, Luc

2009-05-01

We carried out a small-scale laboratory diffusion experiment on a disk-like sample of Opalinus clay from the Mont Terri underground laboratory (Switzerland) using 134Cs as tracer. A through-diffusion phase was followed by an out-diffusion phase where the tracer taken up by the sample was released again. Since the tracer concentration at both boundaries was monitored, careful mass-balance considerations were feasible. A first analysis of the experimental data was done in the frame of a single-species model accounting only for transport and non-linear sorption of caesium. The model could match the data of the through-diffusion phase, however only, when strongly reducing the sorption data based on batch sorption experiments. Yet, such a procedure was in strong contradiction with sorption measurements performed on dispersed and compacted systems. In addition, predictions concerning tracer out-diffusion and mass-balance considerations clearly revealed the shortcomings of this type of model. In a second attempt we applied a multi-species transport model where now the whole water chemistry and a sorption model for caesium were considered. First, the value for the diffusion coefficient was fixed to the best-fit value of the single-species model. But again, the sorption site densities had to be reduced strongly albeit the reduction factor was smaller. Only when fixing the sorption site densities to those values of the sorption model and letting the effective diffusion coefficient D e free for the adjustment, could through-diffusion data be reasonably well fitted and out-diffusion as well as mass-balances be predicted in a satisfying manner. The main results are: (1) The best-fit could be achieved with a value for D e of 1.8 × 10 -10 m 2 s -1 which is rather high but corroborated by results of a molecular modelling study. (2) If caesium arrives in the Opalinus clay sample potassium and sodium (calcium etc.) ions are released and caesium ions are sorbed. The released cations diffuse to lower concentration regions according to their individual concentration gradients. Since locally the cation concentration for potassium, (sodium and calcium) is increased, sorption of these cations is also locally enhanced, affecting in return the sorption behaviour of migrating caesium. Consequently, the sorption process of caesium in such diffusion experiments cannot be addressed by a non-linear isotherm formalism any longer. (3) A reasonable analysis of such single tracer diffusion experiments therefore requires the combined description of transport (diffusion) and sorption of many cations and the whole complex water chemistry of the system. Thus, single-species models can only be applied with care in the considered concentration ranges.

A first-principles and experimental study of helium diffusion in periclase MgO

NASA Astrophysics Data System (ADS)

Song, Zhewen; Wu, Henry; Shu, Shipeng; Krawczynski, Mike; Van Orman, James; Cherniak, Daniele J.; Bruce Watson, E.; Mukhopadhyay, Sujoy; Morgan, Dane

2018-02-01

The distribution of He isotopes is used to trace heterogeneities in the Earth's mantle, and is particularly useful for constraining the length scale of heterogeneity due to the generally rapid diffusivity of helium. However, such an analysis is challenging because He diffusivities are largely unknown in lower mantle phases, which can influence the He profiles in regions that cycle through the lower mantle. With this motivation, we have used first-principles simulations based on density functional theory to study He diffusion in MgO, an important lower mantle phase. We first studied the case of interstitial helium diffusion in perfect MgO and found a migration barrier of 0.73 eV at zero pressure. Then we used the kinetic Monte Carlo method to study the case of substitutional He diffusion in MgO, where we assumed that He diffuses on the cation sublattice through cation vacancies. We also performed experiments on He diffusion at atmospheric pressure using ion implantation and nuclear reaction analysis in both as-received and Ga-doped samples. A comparison between the experimental and simulation results are shown. This work provides a foundation for further studies at high-pressure.

Extraordinary Effects of Specific Monovalent Cations on Activation of Reovirus Transcriptase by Chymotrypsin In Vitro

PubMed Central

Borsa, J.; Sargent, M. D.; Long, D. G.; Chapman, J. D.

1973-01-01

Activation of reovirus transcriptase activity, latent in intact virions, by digestion of purified virions with chymotrypsin (CHT) in vitro shows a stringent requirement for specific monovalent cations. Cs+, Rb+, or K+ ions are capable of facilitating activation by chymotryptic digestion. Na+, Li+, or NH4+ ions are not capable of facilitating the CHT activation of polymerase activity and are antagonistic towards the effects of the facilitating ions. The data indicate that the effect of the cations is exerted on activation of the polymerase activity by CHT as opposed to an effect on polymerization per se. This effect may be important biologically in that it provides a mechanism whereby the virion can sense whether it is in an intracellular or an extracellular environment and thereby can avoid premature uncoating. PMID:4347424

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perriot, Romain; Dholabhai, Pratik P.; Uberuaga, Blas P.

In this paper, we use molecular dynamics simulations to investigate the role of grain boundaries (GBs) on ionic diffusion in pyrochlores, as a function of the GB type, chemistry of the compound, and level of cation disorder. We observe that the presence of GBs promotes oxygen transport in ordered and low-disordered systems, as the GBs are found to have a higher concentration of mobile carriers with higher mobilities than in the bulk. Thus, in ordered samples, the ionic diffusion is 2D, localized along the grain boundary. When cation disorder is introduced, bulk carriers begin to contribute to the overall diffusion,more » while the GB contribution is only slightly enhanced. In highly disordered samples, the diffusive behavior at the GBs is bulk-like, and the two contributions (bulk vs. GB) can no longer be distinguished. There is thus a transition from 2D/GB dominated oxygen diffusivity to 3D/bulk dominated diffusivity versus disorder in pyrochlores. Finally, these results provide new insights into the possibility of using internal interfaces to enhance ionic conductivity in nanostructured complex oxides.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jain, Richa Naja, E-mail: ltprichanaja@gmail.com; Chakraborty, Brahmananda; Ramaniah, Lavanya M.

In this work our main objective is to compute Dynamical correlations, Onsager coefficients and Maxwell-Stefan (MS) diffusivities for molten salt LiF-KF mixture at various thermodynamic states through Green–Kubo formalism for the first time. The equilibrium molecular dynamics (MD) simulations were performed using BHM potential for LiF–KF mixture. The velocity autocorrelations functions involving Li ions reflect the endurance of cage dynamics or backscattering with temperature. The magnitude of Onsager coefficients for all pairs increases with increase in temperature. Interestingly most of the Onsager coefficients has almost maximum magnitude at the eutectic composition indicating the most dynamic character of the eutectic mixture.more » MS diffusivity hence diffusion for all ion pairs increases in the system with increasing temperature. Smooth variation of the diffusivity values denies any network formation in the mixture. Also, the striking feature is the noticeable concentration dependence of MS diffusivity between cation-cation pair, Đ{sub Li-K} which remains negative for most of the concentration range but changes sign to become positive for higher LiF concentration. The negative MS diffusivity is acceptable as it satisfies the non-negative entropy constraint governed by 2{sup nd} law of thermodynamics. This high diffusivity also vouches the candidature of molten salt as a coolant.« less

Effect of water on structure and dynamics of [BMIM][PF6] ionic liquid: An all-atom molecular dynamics simulation investigation.

PubMed

Sharma, Anirban; Ghorai, Pradip Kr

2016-03-21

Composition dependent structural and dynamical properties of aqueous hydrophobic 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6]) ionic liquid (IL) have been investigated by using all-atom molecular dynamics simulation. We observe that addition of water does not increase significant number of dissociated ions in the solution over the pure state. As a consequence, self-diffusion coefficient of the cation and anion is comparable to each other at all water concentration similar to that is observed for the pure state. Voronoi polyhedra analysis exhibits strong dependence on the local environment of IL concentration. Void and neck distributions in Voronoi tessellation are approximately Gaussian for pure IL but upon subsequent addition of water, we observe deviation from the Gaussian behaviour with an asymmetric broadening with long tail of exponential decay at large void radius, particularly at higher water concentrations. The increase in void space and neck size at higher water concentration facilitates ionic motion, thus, decreasing dynamical heterogeneity and IL reorientation time and increases self-diffusion coefficient significantly.

Effect of water on structure and dynamics of [BMIM][PF{sub 6}] ionic liquid: An all-atom molecular dynamics simulation investigation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sharma, Anirban; Ghorai, Pradip Kr., E-mail: pradip@iiserkol.ac.in

2016-03-21

Composition dependent structural and dynamical properties of aqueous hydrophobic 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF{sub 6}]) ionic liquid (IL) have been investigated by using all-atom molecular dynamics simulation. We observe that addition of water does not increase significant number of dissociated ions in the solution over the pure state. As a consequence, self-diffusion coefficient of the cation and anion is comparable to each other at all water concentration similar to that is observed for the pure state. Voronoi polyhedra analysis exhibits strong dependence on the local environment of IL concentration. Void and neck distributions in Voronoi tessellation are approximately Gaussian for pure ILmore » but upon subsequent addition of water, we observe deviation from the Gaussian behaviour with an asymmetric broadening with long tail of exponential decay at large void radius, particularly at higher water concentrations. The increase in void space and neck size at higher water concentration facilitates ionic motion, thus, decreasing dynamical heterogeneity and IL reorientation time and increases self-diffusion coefficient significantly.« less

Simultaneous Extraction of Lithium and Hydrogen from Seawater

DTIC Science & Technology

2011-04-26

chromatography . Anions were analyzed by Anion Ion Chromatography (Instrument Dionex ICS-1500, Column Dionex AS9-HC; AG9-HC Guard, eluent: 9.00 mM Na2CO3, flow...rate: 1.25 mL/min, and sample loop was 25 μL). Cations were analyzed by Cation Ion Chromatography (Instrument Dionex DX-500, Cation Column Dionex ...the amount was measured volumetrically. Ion chromatography : Ions in seawater diffused from/to the anode and cathode were determined by ion

Maxwell-Stefan diffusion and dynamical correlation in molten LiF-KF: A molecular dynamics study

NASA Astrophysics Data System (ADS)

Jain, Richa Naja; Chakraborty, Brahmananda; Ramaniah, Lavanya M.

2016-05-01

In this work our main objective is to compute Dynamical correlations, Onsager coefficients and Maxwell-Stefan (MS) diffusivities for molten salt LiF-KF mixture at various thermodynamic states through Green-Kubo formalism for the first time. The equilibrium molecular dynamics (MD) simulations were performed using BHM potential for LiF-KF mixture. The velocity autocorrelations functions involving Li ions reflect the endurance of cage dynamics or backscattering with temperature. The magnitude of Onsager coefficients for all pairs increases with increase in temperature. Interestingly most of the Onsager coefficients has almost maximum magnitude at the eutectic composition indicating the most dynamic character of the eutectic mixture. MS diffusivity hence diffusion for all ion pairs increases in the system with increasing temperature. Smooth variation of the diffusivity values denies any network formation in the mixture. Also, the striking feature is the noticeable concentration dependence of MS diffusivity between cation-cation pair, ĐLi-K which remains negative for most of the concentration range but changes sign to become positive for higher LiF concentration. The negative MS diffusivity is acceptable as it satisfies the non-negative entropy constraint governed by 2nd law of thermodynamics. This high diffusivity also vouches the candidature of molten salt as a coolant.

Obtaining the porewater composition of a clay rock by modeling the in- and out-diffusion of anions and cations from an in-situ experiment.

PubMed

Appelo, C A J; Vinsot, A; Mettler, S; Wechner, S

2008-10-23

A borehole in the Callovo-Oxfordian clay rock in ANDRA's underground research facility was sampled during 1 year and chemically analyzed. Diffusion between porewater and the borehole solution resulted in concentration changes which were modeled with PHREEQC's multicomponent diffusion module. In the model, the clay rock's pore space is divided in free porewater (electrically neutral) and diffuse double layer water (devoid of anions). Diffusion is calculated separately for the two domains, and individually for all the solute species while a zero-charge flux is maintained. We explain how the finite difference formulas for radial diffusion can be translated into mixing factors for solutions. Operator splitting is used to calculate advective flow and chemical reactions such as ion exchange and calcite dissolution and precipitation. The ion exchange reaction is formulated in the form of surface complexation, which allows distributing charge over the fixed sites and the diffuse double layer. The charge distribution affects pH when calcite dissolves, and modeling of the experimental data shows that about 7% of the cation exchange capacity resides in the diffuse double layer. The model calculates the observed concentration changes very well and provides an estimate of the pristine porewater composition in the clay rock.

Enhanced energy harvesting by concentration gradient-driven ion transport in SBA-15 mesoporous silica thin films.

PubMed

Hwang, Junho; Kataoka, Sho; Endo, Akira; Daiguji, Hirofumi

2016-09-21

Nanofluidic energy harvesting systems have attracted interest in the field of battery application, particularly for miniaturized electrical devices, because they possess excellent energy conversion capability for their size. In this study, a mesoporous silica (MPS)-based nanofluidic energy harvesting system was fabricated and selective ion transport in mesopores as a function of the salt gradient was investigated. Aqueous solutions with three different kinds of monovalent electrolytes-KCl, NaCl, and LiCl-with different diffusion coefficients (D + ) were considered. The highest power density was 3.90 W m -2 for KCl, followed by 2.39 W m -2 for NaCl and 1.29 W m -2 for LiCl. Furthermore, the dependency of power density on the type of cation employed indicates that the harvested energy increases as the cation mobility increases, particularly at high concentrations. This cation-specific dependency suggests that the maximum power density increases by increasing the diffusion coefficient ratio of cations to anions, making this ratio a critical parameter in enhancing the performance of nanofluidic energy harvesting systems with extremely small pores ranging from 2 to 3 nm.

In vitro biopharmaceutical evaluation of ciprofloxacin/metal cation complexes for pulmonary administration.

PubMed

Brillault, J; Tewes, F; Couet, W; Olivier, J C

2017-01-15

Pulmonary delivery of fluoroquinolones (FQs) is an interesting approach to treat lung infections as it may lead to high local concentrations while minimizing systemic exposure. However, FQs have a rapid diffusion through the lung epithelium giving the pulmonary route no advantage compared to the oral route. Interactions between FQs and metal cations form complexes which limit the diffusion through the epithelial barrier and would reduce the absorption of FQs and maintain high concentrations in the lung. The effects of this complexation depend on the FQ and the metal cations and optimum partners should be selected through in vitro experiments prior to aerosol drug formulation. In this study, CIP was chosen as a representative FQ and 5 cations (Ca 2+ , Mg 2+ , Zn 2+ , Al 3+ , Cu 2+ ) were selected to study the complexation and its effects on permeability, antimicrobial efficacy and cell toxicity. The results showed that the apparent association constants between CIP and cations ranked with the descending order: Cu 2+ >Al 3+ >Zn 2+ >Mg 2+ >Ca 2+ . When a target of 80% complexation was reached with the adequate concentrations of cations, the CIP permeability through the Calu-3 lung epithelial cells was decreased of 50%. Toxicity of the CIP on the Calu-3 cells, with an EC50 evaluated at 7μM, was not significantly affected by the presence of the cations. The minimum inhibitory concentration of CIP for Pseudomonas aeruginosa was not affected or slightly increased in the range of cation concentrations tested, except for Mg 2+ . In conclusion, permeability was the main parameter that was affected by the metal cation complexation while cell toxicity and antimicrobial activity were not or slightly modified. Cu 2+ , with the highest apparent constant of association and with no effect on cell toxicity and antimicrobial activity of the CIP, appeared as a promising cation for the development of a controlled-permeability formulation of CIP for lung treatment. Copyright © 2016 Elsevier B.V. All rights reserved.

Kinetics and Mechanisms of Chemical and Biological Agents Release from Biopolymeric Microcapsules.

PubMed

Vinceković, Marko; Jurić, Slaven; Đermić, Edyta; Topolovec-Pintarić, Snježana

2017-11-08

Kinetics and mechanisms of copper cations and Trichoderma viride spores release from uncoated and chitosan coated alginate microcapsules were investigated. The gelation of a fixed amount of sodium alginate at different concentrations of copper ion solutions resulted in distinct kinetics and release mechanisms. The increase in copper cation concentration promoted, but the presence of the chitosan layer on the microcapsule surface and the increase in microcapsule size reduced the rate of active agent release. Fitting to simple Korsmeyer-Peppas empirical model revealed that the underlying release mechanism (Fickian diffusion or a combination of the diffusion and erosion mechanisms) depends on the copper cation concentration and presence of T. viride spores. The investigation pointed out that the proper selection of formulation variables helps in designing microcapsules with the desirable release of copper ions and T. viride for plant protection and nutrition.

Diffusion in the system K2O-SrO-SiO2. II - Cation self-diffusion coefficients.

NASA Technical Reports Server (NTRS)

Varshneya, A. K.; Cooper, A. R.

1972-01-01

The self-diffusion coefficients were measured by introducing a slab of glass previously irradiated in a reactor between two slabs of unirradiated glass. By heating the specimens, etching them sequentially and determining the radioactivity, self-diffusion coefficients for K and Sr were measured. It is pointed out that the results obtained in the investigations appear to support the proposal that the network of the base glass predominantly controls the activation energy for the diffusion of ions.

Empirical constraints on closure temperatures from a single diffusion coefficient

NASA Astrophysics Data System (ADS)

Lee, J. K. W.

The elucidation of thermal histories by geochronological and isotopic means is based fundamentally on solid-state diffusion and the concept of closure temperatures. Because diffusion is thermally activated, an analytical solution of the closure temperature (Tc*) can only be obtained if the diffusion coefficient D of the diffusion process is measured at two or more different temperatures. If the diffusion coefficient is known at only one temperature, however, the true closure temperature (Tc*) cannot be calculated analytically because there exist an infinite number of possible (apparent) closure temperatures (Tc) which can be generated by this single datum. By introducing further empirical constraints to limit the range of possible closure temperatures, however, mathematical analysis of a modified form of the closure temperature equation shows that it is possible to make both qualitative and quantitative estimates of Tc* given knowledge of only one diffusion coefficient DM measured at one temperature TM. Qualitative constraints of the true closure temperature Tc* are obtained from the shapes of curves on a graph of the apparent Tc (Tc) vs. activation energy E, in which each curve is based on a single diffusion coefficient measurement DM at temperature TM. Using a realistic range of E, the concavity of the curve shows whether TM is less than, approximately equal to, or greater than Tc*. Quantitative estimates are obtained by considering two dimensionless parameters [lnÊRT^c vs. Tc*/TM] derived from these curves. When these parameters are plotted for known argon diffusion data and for a given diffusion size and cooling rate, it is found that the resultant curves are almost identical for all of the commonly dated K-Ar minerals - biotite, phlogopite, muscovite, hornblende and orthoclase - in spite of differences in their diffusion parameters. A common curve for Ar diffusion can be derived by least-squares fitting of all the Ar diffusion data and provides a way of predicting a ``model'' closure temperature Tcm from a single diffusion coefficient DM at temperature TM. Preliminary diffusion data for a labradorite lead to a Tcm of 507+/-17°C and a corresponding activation energy of about 65kcal/mol, given a grain size of 200μm and a cooling rate of 5°C/Ma. Curves for He diffusion in silicates (augite, quartz and sanidine) also overlap to a significant degree, both among themselves and with the Ar model curve, suggesting that a single model curve may be a good representation of noble gas closure temperatures in silicates. An analogous model curve for a selection of 18O data can also be constructed, but this curve differs from the Ar model curve. A single model curve for cationic species does not appear to exist, however, suggesting that chemical bonding relationships between the ionic size/charge and crystal structure may influence the closure temperatures of diffusing cations. An indication of the degree of overlap among the various curves for Ar, He, 18O and cations is also obtained by considering the dimensionless parameter E/RTc*; for the noble gases and 18O, E/RTc* values for the respective minerals are very similar, whereas for cations, there is significant dispersion. Given these constraints, this may be a potential method of estimating closure temperatures for certain diffusing species when there are limited diffusion data.

Role of Electrostatic Interactions on the Transport of Druglike Molecules in Hydrogel-Based Articular Cartilage Mimics: Implications for Drug Delivery.

PubMed

Ye, Fengbin; Baldursdottir, Stefania; Hvidt, Søren; Jensen, Henrik; Larsen, Susan W; Yaghmur, Anan; Larsen, Claus; Østergaard, Jesper

2016-03-07

In the field of drug delivery to the articular cartilage, it is advantageous to apply artificial tissue models as surrogates of cartilage for investigating drug transport and release properties. In this study, artificial cartilage models consisting of 0.5% (w/v) agarose gel containing 0.5% (w/v) chondroitin sulfate or 0.5% (w/v) hyaluronic acid were developed, and their rheological and morphological properties were characterized. UV imaging was utilized to quantify the transport properties of the following four model compounds in the agarose gel and in the developed artificial cartilage models: H-Ala-β-naphthylamide, H-Lys-Lys-β-naphthylamide, lysozyme, and α-lactalbumin. The obtained results showed that the incorporation of the polyelectrolytes chondroitin sulfate or hyaluronic acid into agarose gel induced a significant reduction in the apparent diffusivities of the cationic model compounds as compared to the pure agarose gel. The decrease in apparent diffusivity of the cationic compounds was not caused by a change in the gel structure since a similar reduction in apparent diffusivity was not observed for the net negatively charged protein α-lactalbumin. The apparent diffusivity of the cationic compounds in the negatively charged hydrogels was highly dependent on the ionic strength, pointing out the importance of electrostatic interactions between the diffusant and the polyelectrolytes. Solution based affinity studies between the model compounds and the two investigated polyelectrolytes further confirmed the electrostatic nature of their interactions. The results obtained from the UV imaging diffusion studies are important for understanding the effect of drug physicochemical properties on the transport in articular cartilage. The extracted information may be useful in the development of hydrogels for in vitro release testing having features resembling the articular cartilage.

Protic ammonium carboxylate ionic liquids: insight into structure, dynamics and thermophysical properties by alkyl group functionalization.

PubMed

Reddy, Th Dhileep N; Mallik, Bhabani S

2017-04-19

This study is aimed at characterising the structure, dynamics and thermophysical properties of five alkylammonium carboxylate ionic liquids (ILs) from classical molecular dynamics simulations. The structural features of these ILs were characterised by calculating the site-site radial distribution functions, g(r), spatial distribution functions and structure factors. The structural properties demonstrate that ILs show greater interaction between cations and anions when alkyl chain length increases on the cation or anion. In all ILs, spatial distribution functions show that the anion is close to the acidic hydrogen atoms of the ammonium cation. We determined the role of alkyl group functionalization of the charged entities, cations and anions, in the dynamical behavior and the transport coefficients of this family of ionic liquids. The dynamics of ILs are described by studying the mean square displacement (MSD) of the centres of mass of the ions, diffusion coefficients, ionic conductivities and hydrogen bonds as well as residence dynamics. The diffusion coefficients and ionic conductivity decrease with an increase in the size of the cation or anion. The effect of alkyl chain length on ionic conductivity calculated in this article is consistent with the findings of other experimental studies. Hydrogen bond lifetimes and residence times along with structure factors were also calculated, and are related to alkyl chain length.

Structural changes of polyacids initiated by their neutralization with various alkali metal hydroxides. Diffusion studies in poly(acrylic acid)s.

PubMed

Masiak, Michal; Hyk, Wojciech; Stojek, Zbigniew; Ciszkowska, Malgorzata

2007-09-27

The changes in the three-dimensional structure of the poly(acrylic acid), PAA, induced by incorporation of various alkali-metal counterions have been evaluated by studying diffusion of an uncharged probe (1,1'-ferrocenedimethanol) in the polymeric media. The studies are supported by the measurements of conductivity and viscosity of the polymeric media. Solutions of linear PAA of four different sizes (molecular weights: 450,000, 750,000, 1,250,000, 4,000,000) were neutralized with hydroxides of alkali metals of group 1 of the periodic table (Li, Na, K, Rb, Cs) to the desired neutralization degree. The transport properties of the obtained polyacrylates were monitored by measuring the changes in the probe diffusion coefficient during the titration of the polyacids. The probe diffusivity was determined from the steady-state current of the probe voltammetric oxidation at disk microelectrodes. Diffusivity of the probe increases with the increase in the degree of neutralization and with the increase in viscosity. It reaches the maximum value at about 60-80% of the polyacid neutralization. The way the probe diffusion coefficients change is similar in all polyacid solutions and gels. The increase in the size of a metal cation causes, in general, an enhancement in the transport of probe molecules. The biggest differences in the probe diffusivities are between lithium and cesium polyacrylates. The differences between the results obtained for cesium and rubidium are not statistically significant due to lack of good precision of the voltammetric measurements. The measurements of the electric conductivity of polyacrylates and the theoretical predictions supplemented the picture of electrostatic interactions between the polyanionic chains and the metal cations of increasing size. In all instances of the PAAs, the viscosity of the solutions rapidly increases in the 0-60% range of neutralization and then becomes constant in the 60-100% region. With the exception of the shortest chain polyacid, the formation of a rigid medium (gel) has been observed in the experiments with all cations. After the end point of the titration was passed, a sudden drop in the viscosity and the disappearance of the gelatinous structure were seen. The largest value of viscosity has been recorded for the longest chain polyacid. The change in the cation of the strong base used did not affect the viscosity of the polymeric system.

Investigation of local environments in Nafion-SiO(2) composite membranes used in vanadium redox flow batteries.

PubMed

Vijayakumar, M; Schwenzer, Birgit; Kim, Soowhan; Yang, Zhenguo; Thevuthasan, S; Liu, Jun; Graff, Gordon L; Hu, Jianzhi

2012-04-01

Proton conducting polymer composite membranes are of technological interest in many energy devices such as fuel cells and redox flow batteries. In particular, polymer composite membranes, such as SiO(2) incorporated Nafion membranes, are recently reported as highly promising for the use in redox flow batteries. However, there is conflicting reports regarding the performance of this type of Nafion-SiO(2) composite membrane in the redox flow cell. This paper presents results of the analysis of the Nafion-SiO(2) composite membrane used in a vanadium redox flow battery by nuclear magnetic resonance (NMR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier Transform Infra Red (FTIR) spectroscopy, and ultraviolet-visible spectroscopy. The XPS study reveals the chemical identity and environment of vanadium cations accumulated at the surface. On the other hand, the (19)F and (29)Si NMR measurement explores the nature of the interaction between the silica particles, Nafion side chains and diffused vanadium cations. The (29)Si NMR shows that the silica particles interact via hydrogen bonds with the sulfonic groups of Nafion and the diffused vanadium cations. Based on these spectroscopic studies, the chemical environment of the silica particles inside the Nafion membrane and their interaction with diffusing vanadium cations during flow cell operations are discussed. This study discusses the origin of performance degradation of the Nafion-SiO(2) composite membrane materials in vanadium redox flow batteries. Copyright © 2011 Elsevier Inc. All rights reserved.

MD simulations of the formation of stable clusters in mixtures of alkaline salts and imidazolium-based ionic liquids.

PubMed

Méndez-Morales, Trinidad; Carrete, Jesús; Bouzón-Capelo, Silvia; Pérez-Rodríguez, Martín; Cabeza, Óscar; Gallego, Luis J; Varela, Luis M

2013-03-21

Structural and dynamical properties of room-temperature ionic liquids containing the cation 1-butyl-3-methylimidazolium ([BMIM](+)) and three different anions (hexafluorophosphate, [PF6](-), tetrafluoroborate, [BF4](-), and bis(trifluoromethylsulfonyl)imide, [NTf2](-)) doped with several molar fractions of lithium salts with a common anion at 298.15 K and 1 atm were investigated by means of molecular dynamics simulations. The effect of the size of the salt cation was also analyzed by comparing these results with those for mixtures of [BMIM][PF6] with NaPF6. Lithium/sodium solvation and ionic mobilities were analyzed via the study of radial distribution functions, coordination numbers, cage autocorrelation functions, mean-square displacements (including the analysis of both ballistic and diffusive regimes), self-diffusion coefficients of all the ionic species, velocity and current autocorrelation functions, and ionic conductivity in all the ionic liquid/salt systems. We found that lithium and sodium cations are strongly coordinated in two different positions with the anion present in the mixture. Moreover, [Li](+) and [Na](+) cations were found to form bonded-like, long-lived aggregates with the anions in their first solvation shell, which act as very stable kinetic entities within which a marked rattling motion of salt ions takes place. With very long MD simulation runs, this phenomenon is proved to be on the basis of the decrease of self-diffusion coefficients and ionic conductivities previously reported in experimental and computational results.

Investigation of Local Environments in Nafion-SiO2 Composite Membranes used in Vanadium Redox Flow Batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vijayakumar, M.; Schwenzer, Birgit; Kim, Soowhan

2012-04-01

The proton conducting polymer composite membranes are of technological interest in many energy devices such as fuel cells and redox flow batteries. In particular, the polymer composite membranes such as SiO2 incorporated Nafion membranes are recently reported as highly promising for the redox flow batteries. However, there is conflicting reports regarding the performance of this Nafion-SiO2 composite membrane in the redox flow cell. This paper presents results of the analysis of the Nafion-SiO2 composite membrane used in a vanadium redox flow battery by nuclear magnetic resonance (NMR) spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier Transformed Infra Red (FTIR) spectroscopy, and ultravioletmore » visible spectroscopy. The XPS study reveals the chemical identity and environment of vanadium cations accumulated at the surface. On the other hand, the 19F and 29Si NMR measurement explores the nature of the interaction between the silica particles, Nafion side chains and diffused vanadium cations. The 29Si NMR shows that the silica particles interaction via hydrogen bonds to the sulfonic groups of Nafion and diffused vanadium cations. Based on these spectroscopic studies, the chemical environment of the silica particles inside the Nafion membrane and their interaction with diffusing vanadium cations during flow cell operations are discussed. This study discusses the origin of performance degradation of the Nafion-SiO2 composite membrane materials in vanadium redox flow batteries.« less

Water diffusion in silicate glasses: the effect of glass structure

NASA Astrophysics Data System (ADS)

Kuroda, M.; Tachibana, S.

2016-12-01

Water diffusion in silicate melts (glasses) is one of the main controlling factors of magmatism in a volcanic system. Water diffusivity in silicate glasses depends on its own concentration. However, the mechanism causing those dependences has not been fully understood yet. In order to construct a general model for water diffusion in various silicate glasses, we performed water diffusion experiments in silica glass and proposed a new water diffusion model [Kuroda et al., 2015]. In the model, water diffusivity is controlled by the concentration of both main diffusion species (i.e. molecular water) and diffusion pathways, which are determined by the concentrations of hydroxyl groups and network modifier cations. The model well explains the water diffusivity in various silicate glasses from silica glass to basalt glass. However, pre-exponential factors of water diffusivity in various glasses show five orders of magnitude variations although the pre-exponential factor should ideally represent the jump frequency and the jump distance of molecular water and show a much smaller variation. Here, we attribute the large variation of pre-exponential factors to a glass structure dependence of activation energy for molecular water diffusion. It has been known that the activation energy depends on the water concentration [Nowak and Behrens, 1997]. The concentration of hydroxyls, which cut Si-O-Si network in the glass structure, increases with water concentration, resulting in lowering the activation energy for water diffusion probably due to more fragmented structure. Network modifier cations are likely to play the same role as water. With taking the effect of glass structure into account, we found that the variation of pre-exponential factors of water diffusivity in silicate glasses can be much smaller than the five orders of magnitude, implying that the diffusion of molecular water in silicate glasses is controlled by the same atomic process.

Influence of liquid structure on diffusive isotope separation in molten silicates and aqueous solutions

NASA Astrophysics Data System (ADS)

Watkins, James M.; DePaolo, Donald J.; Ryerson, Frederick J.; Peterson, Brook T.

2011-06-01

Molecular diffusion in natural volcanic liquids discriminates between isotopes of major ions (e.g., Fe, Mg, Ca, and Li). Although isotope separation by diffusion is expected on theoretical grounds, the dependence on mass is highly variable for different elements and in different media. Silicate liquid diffusion experiments using simple liquid compositions were carried out to further probe the compositional dependence of diffusive isotopic discrimination and its relationship to liquid structure. Two diffusion couples consisting of the mineral constituents anorthite (CaAl 2Si 2O 8; denoted AN), albite (NaAlSi 3O 8; denoted AB), and diopside (CaMgSi 2O 6; denoted DI) were held at 1450 °C for 2 h and then quenched to ambient pressure and temperature. Major-element as well as Ca and Mg isotope profiles were measured on the recovered quenched glasses. In both experiments, Ca diffuses rapidly with respect to Si. In the AB-AN experiment, D Ca/ D Si ≈ 20 and the efficiency of isotope separation for Ca is much greater than in natural liquid experiments where D Ca/ D Si ≈ 1. In the AB-DI experiment, D Ca/ D Si ≈ 6 and the efficiency of isotope separation is between that of the natural liquid experiments and the AB-AN experiment. In the AB-DI experiment, D Mg/ D Si ≈ 1 and the efficiency of isotope separation for Mg is smaller than it is for Ca yet similar to that observed for Mg in natural liquids. The results from the experiments reported here, in combination with results from natural volcanic liquids, show clearly that the efficiency of diffusive separation of Ca isotopes is systematically related to the solvent-normalized diffusivity - the ratio of the diffusivity of the cation ( D Ca) to the diffusivity of silicon ( D Si). The results on Ca isotopes are consistent with available data on Fe, Li, and Mg isotopes in silicate liquids, when considered in terms of the parameter D cation/ D Si. Cations diffusing in aqueous solutions display a similar relationship between isotopic separation efficiency and Dcation/D, although the efficiencies are smaller than in silicate liquids. Our empirical relationship provides a tool for predicting the magnitude of diffusive isotopic effects in many geologic environments and a basis for a more comprehensive theory of isotope separation in liquid solutions. We present a conceptual model for the relationship between diffusivity and liquid structure that is consistent with available data.

The influence of ionic strength on DNA diffusion in gel networks

NASA Astrophysics Data System (ADS)

Fu, Yuanxi; Jee, Ah-Young; Kim, Hyeong-Ju; Granick, Steve

Cations are known to reduce the rigidity of the DNA molecules by screening the negative charge along the sugar phosphate backbone. This was established by optical tweezer pulling experiment of immobilized DNA strands. However, little is known regarding the influence of ions on the motion of DNA molecules as they thread through network meshes. We imaged in real time the Brownian diffusion of fluorescent labeled lambda-DNA in an agarose gel network in the presence of salt with monovalent or multivalent cations. Each movie was analyzed using home-written program to yield a trajectory of center of the mass and the accompanying history of the shape fluctuations. One preliminary finding is that ionic strength has a profound influence on the slope of the trace of mean square displacement (MSD) versus time. The influence of ionic strength on DNA diffusion in gel networks.

Cation-Dependent Gold Recovery with α-Cyclodextrin Facilitated by Second-Sphere Coordination.

PubMed

Liu, Zhichang; Samanta, Avik; Lei, Juying; Sun, Junling; Wang, Yuping; Stoddart, J Fraser

2016-09-14

Herein, we report an alkali metal cation-dependent approach to gold recovery, facilitated by second-sphere coordination with eco-friendly α-cyclodextrin (α-CD). Upon mixing eight salts composed of Na(+), K(+), Rb(+), or Cs(+) cations and [AuX4](-) (X = Cl/Br) anions with α-, β-, or γ-CD in water, co-precipitates form selectively from the three (out of 24) aqueous solutions containing α-CD with KAuBr4, RbAuBr4, and CsAuBr4, from which the combination of α-CD and KAuBr4 affords the highest yield. Single-crystal X-ray analyses reveal that in 20 of the 24 adducts CD and [AuX4](-) anions form 2:1 sandwich-type second-sphere adducts driven partially by [C-H···X-Au] interactions between [AuX4](-) anions and the primary faces of two neighboring CDs. In the adduct formed between α-CD and KAuBr4, a [K(OH2)6](+) cation is encapsulated inside the cavity between the secondary faces of two α-CDs, leading to highly efficient precipitation owing to the formation of a cation/anion alternating ion wire residing inside a continuous α-CD nanotube. By contrast, in the other 19 adducts, the cations are coordinated by OH groups and glucopyranosyl ring O atoms in CDs. The strong coordination of Rb(+) and Cs(+) cations by these ligands, in conjunction with the stereoelectronically favorable binding of [AuBr4](-) anions with two α-CDs, facilitates the co-precipitation of the two adducts formed between α-CD with RbAuBr4 and CsAuBr4. In order to develop an efficient process for green gold recovery, the co-precipitation yield of α-CD and KAuBr4 has been optimized regarding both the temperature and the molar ratio of α-CD to KAuBr4.

In vitro investigation of intestinal transport mechanism of silicon, supplied as orthosilicic acid-vanillin complex.

PubMed

Sergent, Thérèse; Croizet, Karine; Schneider, Yves-Jacques

2017-02-01

Silicon (Si) is one of the most abundant trace elements in the body. Although pharmacokinetics data described its absorption from the diet and its body excretion, the mechanisms involved in the uptake and transport of Si across the gut wall have not been established. Caco-2 cells were used as a well-accepted in vitro model of the human intestinal epithelium to investigate the transport, across the intestinal barrier in both the absorption and excretion directions, of Si supplied as orthosilicic acid stabilized by vanillin complex (OSA-VC). The transport of this species was found proportional to the initial concentration and to the duration of incubation, with absorption and excretion mean rates similar to those of Lucifer yellow, a marker of paracellular diffusion, and increasing in the presence of EGTA, a chelator of divalents cations including calcium. A cellular accumulation of Si, polarized from the apical side of cells, was furthermore detected. These results provide evidence that Si, ingested as a food supplement containing OSA-VC, crosses the intestinal mucosa by passive diffusion via the paracellular pathway through the intercellular tight junctions and accumulates intracellularly, probably by an uptake mechanism of facilitated diffusion. This study can help to further understand the kinetic of absorption of Si. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Simulating Donnan equilibria based on the Nernst-Planck equation

NASA Astrophysics Data System (ADS)

Gimmi, Thomas; Alt-Epping, Peter

2018-07-01

Understanding ion transport through clays and clay membranes is important for many geochemical and environmental applications. Ion transport is affected by electrostatic forces exerted by charged clay surfaces. Anions are partly excluded from pore water near these surfaces, whereas cations are enriched. Such effects can be modeled by the Donnan approach. Here we introduce a new, comparatively simple way to represent Donnan equilibria in transport simulations. We include charged surfaces as immobile ions in the balance equation and calculate coupled transport of all components, including the immobile charges, with the Nernst-Planck equation. This results in an additional diffusion potential that influences ion transport, leading to Donnan ion distributions while maintaining local charge balance. The validity of our new approach was demonstrated by comparing Nernst-Planck simulations using the reactive transport code Flotran with analytical solutions available for simple Donnan systems. Attention has to be paid to the numerical evaluation of the electrochemical migration term in the Nernst-Planck equation to obtain correct results for asymmetric electrolytes. Sensitivity simulations demonstrate the influence of various Donnan model parameters on simulated anion accessible porosities. It is furthermore shown that the salt diffusion coefficient in a Donnan pore depends on local concentrations, in contrast to the aqueous salt diffusion coefficient. Our approach can be easily implemented into other transport codes. It is versatile and facilitates, for instance, assessing the implications of different activity models for the Donnan porosity.

Role of Reverse Divalent Cation Diffusion in Forward Osmosis Biofouling.

PubMed

Xie, Ming; Bar-Zeev, Edo; Hashmi, Sara M; Nghiem, Long D; Elimelech, Menachem

2015-11-17

We investigated the role of reverse divalent cation diffusion in forward osmosis (FO) biofouling. FO biofouling by Pseudomonas aeruginosa was simulated using pristine and chlorine-treated thin-film composite polyamide membranes with either MgCl2 or CaCl2 draw solution. We related FO biofouling behavior-water flux decline, biofilm architecture, and biofilm composition-to reverse cation diffusion. Experimental results demonstrated that reverse calcium diffusion led to significantly more severe water flux decline in comparison with reverse magnesium permeation. Unlike magnesium, reverse calcium permeation dramatically altered the biofilm architecture and composition, where extracellular polymeric substances (EPS) formed a thicker, denser, and more stable biofilm. We propose that FO biofouling was enhanced by complexation of calcium ions to bacterial EPS. This hypothesis was confirmed by dynamic and static light scattering measurements using extracted bacterial EPS with the addition of either MgCl2 or CaCl2 solution. We observed a dramatic increase in the hydrodynamic radius of bacterial EPS with the addition of CaCl2, but no change was observed after addition of MgCl2. Static light scattering revealed that the radius of gyration of bacterial EPS with addition of CaCl2 was 20 times larger than that with the addition of MgCl2. These observations were further confirmed by transmission electron microscopy imaging, where bacterial EPS in the presence of calcium ions was globular, while that with magnesium ions was rod-shaped.

Sorption kinetics and isotherm studies of a cationic dye using agricultural waste: broad bean peels.

PubMed

Hameed, B H; El-Khaiary, M I

2008-06-15

In this paper, broad bean peels (BBP), an agricultural waste, was evaluated for its ability to remove cationic dye (methylene blue) from aqueous solutions. Batch mode experiments were conducted at 30 degrees C. Equilibrium sorption isotherms and kinetics were investigated. The kinetic data obtained at different concentrations have been analyzed using pseudo-first-order, pseudo-second-order and intraparticle diffusion equations. The experimental data fitted very well the pseudo-first-order kinetic model. Analysis of the temportal change of q indicates that at the beginning of the process the overall rate of adsorption is controlled by film-diffusion, then at later stage intraparticle-diffusion controls the rate. Diffusion coefficients and times of transition from film to pore-diffusion control were estimated by piecewise linear regression. The experimental data were analyzed by the Langmuir and Freundlich models. The sorption isotherm data fitted well to Langmuir isotherm and the monolayer adsorption capacity was found to be 192.7 mg/g and the equilibrium adsorption constant Ka is 0.07145 l/mg at 30 degrees C. The results revealed that BBP was a promising sorbent for the removal of methylene blue from aqueous solutions.

Do TFSA anions slither? Pressure exposes the role of TFSA conformational exchange in self-diffusion

DOE PAGES

Suarez, Sophia N.; Wishart, James F.; Rua, Armando; ...

2015-10-28

Multi-nuclear ( 1H, 2H, and 19F) magnetic resonance spectroscopy techniques as functions of temperature and pressure were applied to the study of selectively deuterated 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (EMIM TFSA) ionic liquid isotopologues and related ionic liquids. For EMIM TFSA, temperature-dependent 2H T 1 data indicate stronger electric field gradients in the alkyl chain region compared to the imidazolium ring. Most significantly, the pressure dependences of the EMIM and TFSA self-diffusion coefficients revealed that the displacements of the cations and anions are independent, with diffusion of the TFSA anions being slowed much more by increasing pressure than for the EMIM cations, asmore » shown by their respective activation volumes (28.8 ± 2.5 cm³/mol for TFSA vs. 14.6 ± 1.3 cm³/mol for EMIM). Increasing pressure may lower the mobility of the TFSA anion by hindering its interconversion between trans and cis conformers, a process that is coupled to diffusion according to published molecular dynamics simulations. Measured activation volumes (ΔV ‡) for ion self-diffusion in EMIM bis(fluoromethylsulfonyl)amide and EMIM tetrafluoroborate support this hypothesis.« less

Do TFSA anions slither? Pressure exposes the role of TFSA conformational exchange in self-diffusion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Suarez, Sophia N.; Wishart, James F.; Rua, Armando

Multi-nuclear ( 1H, 2H, and 19F) magnetic resonance spectroscopy techniques as functions of temperature and pressure were applied to the study of selectively deuterated 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (EMIM TFSA) ionic liquid isotopologues and related ionic liquids. For EMIM TFSA, temperature-dependent 2H T 1 data indicate stronger electric field gradients in the alkyl chain region compared to the imidazolium ring. Most significantly, the pressure dependences of the EMIM and TFSA self-diffusion coefficients revealed that the displacements of the cations and anions are independent, with diffusion of the TFSA anions being slowed much more by increasing pressure than for the EMIM cations, asmore » shown by their respective activation volumes (28.8 ± 2.5 cm³/mol for TFSA vs. 14.6 ± 1.3 cm³/mol for EMIM). Increasing pressure may lower the mobility of the TFSA anion by hindering its interconversion between trans and cis conformers, a process that is coupled to diffusion according to published molecular dynamics simulations. Measured activation volumes (ΔV ‡) for ion self-diffusion in EMIM bis(fluoromethylsulfonyl)amide and EMIM tetrafluoroborate support this hypothesis.« less

Two-cation competition in ionic-liquid-modified electrolytes for lithium ion batteries.

PubMed

Lee, Sang-Young; Yong, Hyun Hang; Lee, Young Joo; Kim, Seok Koo; Ahn, Soonho

2005-07-21

It is a common observation that when ionic liquids are added to electrolytes the performances of lithium ion cells become poor, while the thermal safeties of the electrolytes might be improved. In this study, this behavior is investigated based on the kinetics of ionic diffusion. As a model ionic liquid, we chose butyldimethylimidazolium hexafluorophosphate (BDMIPF(6)). The common solvent was propylene carbonate (PC), and lithium hexafluorophosphate (LiPF(6)) was selected as the lithium conducting salt. Ionic diffusion coefficients are estimated by using a pulsed field gradient NMR technique. From a basic study on the model electrolytes (BDMIPF(6) in PC, LiPF(6) in PC, and BDMIPF(6) + LiPF(6) in PC), it was found that the BDMI(+) from BDMIPF(6) shows larger diffusion coefficients than the Li(+) from LiPF(6). However, the anionic (PF(6)(-)) diffusion coefficients present little difference between the model electrolytes. The higher diffusion coefficient of BDMI(+) than that of Li(+) suggests that the poor C-rate performance of lithium ion cells containing ionic liquids as an electrolyte component can be attributed to the two-cation competition between Li(+) and BDMI(+).

Communication: Unusual structure and transport in ionic liquid-hexane mixtures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, Min; Khatun, Sufia; Castner, Edward W., E-mail: ecastner@rci.rutgers.edu

2015-03-28

Ionic liquids having a sufficiently amphiphilic cation can dissolve large volume fractions of alkanes, leading to mixtures with intriguing properties on molecular length scales. The trihexyl(tetradecyl)phosphonium cation paired with the bis(trifluoromethylsulfonyl)amide anion provides an ionic liquid that can dissolve large mole fractions of hexane. We present experimental results on mixtures of n-C{sub 6}D{sub 14} with this ionic liquid. High-energy X-ray scattering studies reveal a persistence of the characteristic features of ionic liquid structure even for 80% dilution with n-C{sub 6}D{sub 14}. Nuclear magnetic resonance self-diffusion results reveal decidedly non-hydrodynamic behavior where the self-diffusion of the neutral, non-polar n-C{sub 6}D{sub 14}more » is on average a factor of 21 times faster than for the cation. Exploitation of the unique structural and transport properties of these mixtures may lead to new opportunities for designer solvents for enhanced chemical reactivity and interface science.« less

Photoinduced Bimolecular Electron Transfer in Ionic Liquids: Cationic Electron Donors

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Boning; Liang, Min; Zmich, Nicole

Recently, we have reported a systematic study of photoinduced electron-transfer reactions in ionic liquid solvents using neutral and anionic electron donors and a series of cyano-substituted anthracene acceptors [Wu, B.; Maroncelli, M.; Castner, E. W., Jr.Photoinduced Bimolecular Electron Transfer in Ionic Liquids. J. Am. Chem. Soc.139, 2017, 14568]. In this paper, we report complementary results for a cationic class of 1-alkyl-4-dimethylaminopyridinium electron donors. Reductive quenching of cyano-substituted anthracene fluorophores by these cationic quenchers is studied in solutions of acetonitrile and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Varying the length of the alkyl chain permits tuning of the quencher diffusivities in solution.more » The observed quenching kinetics are interpreted using a diffusion-reaction analysis. Finally, together with results from the prior study, these results show that the intrinsic electron-transfer rate constant does not depend on the quencher charge in this family of reactions.« less

Effect of Aprotic Solvents on the Dynamics of a Room Temperature Ionic Liquid

NASA Astrophysics Data System (ADS)

Osti, Naresh; van Aken, Katherine; Thompson, Matthew; Tiet, Felix; Jiang, De-En; Cummings, Peter; Gogotsi, Yury; Mamontov, Eugene

Room temperature ionic liquids (RTILs) have attracted much attention as electrolytes in energy storage devices because of their peculiar physical and chemical characteristics. However, their remarkably high viscosity, which results in low conductivity and diffusivity, may adversely affect the charging and discharging rates. Despite changing molecular configurations, use of aprotic solvent allows to enhance the transport properties of ionic liquids by disrupting the cation-anion interactions. We explore the impact of dipole moment of aprotic solvents on the cation-anion interaction and transport in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [BMIM +][Tf2N-], RTIL using molecular dynamics (MD) simulations and quasi-elastic neutrons scattering (QENS) measurements. We observed an increase in cation diffusivity with the increasing dipole moment of the solvent. This effect is due to a decrease in the solvation free energy induced by the increasing solvent polarity. A clear nano-phase separation into ionic liquid-rich and ionic liquid-poor phases as observed by QENS will be also discussed.

Communication: Unusual structure and transport in ionic liquid-hexane mixtures

DOE PAGES

Liang, Min; Khatun, Sufia; Castner, Edward W.

2015-03-28

Ionic liquids having a sufficiently amphiphilic cation can dissolve large volume fractions of alkanes, leading to mixtures with intriguing properties on molecular length scales. The trihexyl(tetradecyl)phosphonium cation paired with the bis(trifluoromethylsulfonyl)amide anion provides an ionic liquid that can dissolve large mole fractions of hexane. We present experimental results on mixtures of n-C 6D 14 with this ionic liquid. High- energy X-ray scattering studies reveal a persistence of the characteristic features of ionic liquid structure even for 80% dilution with n-C 6D 14. NMR self-diffusion results reveal decidedly non-hydrodynamic behavior where the self-diffusion of the neutral, non-polar n-C 6D 14 ismore » on average a factor of 21 times faster than for the cation. Exploitation of the unique structural and transport properties of these mixtures may lead to new opportunities for designer solvents for enhanced chemical reactivity and interface science.« less

Photoinduced Bimolecular Electron Transfer in Ionic Liquids: Cationic Electron Donors

DOE PAGES

Wu, Boning; Liang, Min; Zmich, Nicole; ...

2018-01-29

Recently, we have reported a systematic study of photoinduced electron-transfer reactions in ionic liquid solvents using neutral and anionic electron donors and a series of cyano-substituted anthracene acceptors [Wu, B.; Maroncelli, M.; Castner, E. W., Jr.Photoinduced Bimolecular Electron Transfer in Ionic Liquids. J. Am. Chem. Soc.139, 2017, 14568]. In this paper, we report complementary results for a cationic class of 1-alkyl-4-dimethylaminopyridinium electron donors. Reductive quenching of cyano-substituted anthracene fluorophores by these cationic quenchers is studied in solutions of acetonitrile and the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. Varying the length of the alkyl chain permits tuning of the quencher diffusivities in solution.more » The observed quenching kinetics are interpreted using a diffusion-reaction analysis. Finally, together with results from the prior study, these results show that the intrinsic electron-transfer rate constant does not depend on the quencher charge in this family of reactions.« less

Thermodynamics and defect chemistry of substitutional and interstitial cation doping in layered α-V2O5.

PubMed

McColl, Kit; Johnson, Ian; Corà, Furio

2018-05-25

A systematic study of the location and energetics of cation dopants in α-V2O5 has been conducted using pair-potential methods, supplemented by first-principles calculations. The consequences of doping on intrinsic defect equilibria have been discussed and the effects of selected dopants on Li+ and Mg2+ diffusion energy barriers have been investigated.

Physical properties of ionic liquids consisting of the 1-butyl-3-methylimidazolium cation with various anions and the bis(trifluoromethylsulfonyl)imide anion with various cations.

PubMed

Jin, Hui; O'Hare, Bernie; Dong, Jing; Arzhantsev, Sergei; Baker, Gary A; Wishart, James F; Benesi, Alan J; Maroncelli, Mark

2008-01-10

Physical properties of 4 room-temperature ionic liquids consisting of the 1-butyl-3-methylimidazolium cation with various perfluorinated anions and the bis(trifluoromethylsulfonyl)imide (Tf2N-) anion with 12 pyrrolidinium-, ammonium-, and hydroxyl-containing cations are reported. Electronic structure methods are used to calculate properties related to the size, shape, and dipole moment of individual ions. Experimental measurements of phase-transition temperatures, densities, refractive indices, surface tensions, solvatochromic polarities based on absorption of Nile Red, 19F chemical shifts of the Tf2N- anion, temperature-dependent viscosities, conductivities, and cation diffusion coefficients are reported. Correlations among the measured quantities as well as the use of surface tension and molar volume for estimating Hildebrand solubility parameters of ionic liquids are also discussed.

Structure and Dynamics of Ionic Liquid [MMIM][Br] Confined in Hydrophobic and Hydrophilic Porous Matrices: A Molecular Dynamics Simulation Study.

PubMed

Sharma, Anirban; Ghorai, Pradip Kr

2016-11-17

The effects of confinement on the structural and dynamical properties of the ionic liquid (IL) 1,3-dimethylimidazolium bromide ([MMIM][Br]) have been investigated by molecular dynamics simulations. We used zeolite faujasite (NaY) as a hydrophilic confinement and dealuminated faujasite (DAY) as a hydrophobic confinement. The presence of an extra framework cation, [Na + ], in NaY makes the host hydrophilic, whereas DAY, with no extra framework cation, is hydrophobic. Although both NaY and DAY have almost similar structures, the IL showed markedly different structural and dynamical properties in these confinements and in bulk. In the confinements, the cation-cation radial distribution function, which strongly depends on temperature, exhibits a layer-like structure, whereas in bulk, it shows a liquid-like structure that hardly depends on temperature. Although the interaction between [MMIM] + and Br - in DAY is stronger than that in both NaY and bulk, the strength of the interaction between them is almost invariant with temperature. Both [MMIM] + and Br - strongly interact with Na + of the host, and their interaction strongly depends on temperature, whereas the interaction of the IL with Si and O is very weak and invariant with temperature. In bulk, the self-diffusion coefficient, [D], of both [MMIM] + and Br - increases exponentially with temperature, and the D of the cation is slightly higher than that of the anion at all studied temperatures, whereas in the confinements, [MMIM] + moves much faster than Br - . For example, in the hydrophilic confinement, the D of the cation is 20-30 times higher than that of the anion. The D of both the ions decreases significantly in the confinements as compared to that in bulk. During diffusion, [MMIM] + diffuses closer to the inner surface in the hydrophilic confinement than that in the hydrophobic confinement. The diffusion pathway imperceptibly depends on temperature but strongly depends on the nature of the confinement. The self part of the time-dependent van Hoove correlation function of [MMIM] + in the hydrophilic confinement shows a larger deviation from its Gaussian form than that in the hydrophobic confinement at all temperatures, indicating that the long-time dynamics of [MMIM] + in NaY is more heterogeneous than that in DAY. Although the orientational relaxation time scales of [MMIM] + in the confinements significantly slowed as compared to those in bulk, confinement does not affect the librational motion of the collective hydrogen-bond network present in the IL.

Transdermal delivery of biomacromolecules using lipid-like nanoparticles

NASA Astrophysics Data System (ADS)

Bello, Evelyn A.

The transdermal delivery of biomacromolecules, including proteins and nucleic acids, is challenging, owing to their large size and the penetration-resistant nature of the stratum corneum. Thus, an urgent need exists for the development of transdermal delivery methodologies. This research focuses on the use of cationic lipid-like nanoparticles (lipidoids) for the transdermal delivery of proteins, and establishes an in vitro model for the study. The lipidoids used were first combinatorially designed and synthesized; afterwards, they were employed for protein encapsulation in a vesicular system. A skin penetration study demonstrated that lipidoids enhance penetration depth in a pig skin model, overcoming the barrier that the stratum corneum presents. This research has successfully identified active lipidoids capable of efficiently penetrating the skin; therefore, loading proteins into lipidoid nanoparticles will facilitate the transdermal delivery of proteins. Membrane diffusion experiments were used to confirm the results. This research has confirmed that lipidoids are a suitable material for transdermal protein delivery enhancement.

The Correlation of Adsorption Behavior between Ciprofloxacin Hydrochloride and the Active Sites of Fe-doped MCM-41.

PubMed

Wu, Ying; Tang, Yiming; Li, Laisheng; Liu, Peihong; Li, Xukai; Chen, Weirui; Xue, Ying

2018-01-01

HIGHLIGHTS Fe incorporation significantly accelerated the adsorption of CPX on MCM-41.Fe leaching can be ignored when pH was higher than 4.0.pH played an important role in CPX adsorption on Fe-MCM-41.Co-effect of CPX and metal cations on Fe-MCM-41 was investigated. Fe-MCM-41s with various molar ratios of silicon to iron (20, 40, 80, and 160) were prepared to investigate adsorption properties of ciprofloxacin hydrochloride (CPX) in aqueous solutions. Fe-MCM-41s were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption isotherms, and infrared spectroscopy (FT-IR). Effects of silicon-iron ratio, adsorbent dosage, pH, and temperature were conducted to explore the adsorption mechanism of CPX on Fe-MCM-41. The results showed that the introduction of iron facilitated the absorption quantity for CPX from 20.04 to 83.33 mg g -1 at 120 min of reaction time, which was mainly attributed to surface complexation. The promotion of hydrophobic effect, electrostatic interactions, and π-π electron donor-acceptor interaction also played coordinate roles in the adsorption process. The experimental kinetic data followed both the pseudo-second-order and intra-particle diffusion models, while the adsorption isotherm data fit well to Freundlich model at high temperature. Thermodynamic study showed that the adsorption was spontaneous. Under the effect of electrostatic interaction, pH of the solution strongly affected CPX adsorption. Five representative metal cations (Ca, Cu, Ni, Pb, and Cd) were chosen to study the effects on CPX adsorption and their complexation. The inhibiting effect of metal cations on CPX adsorption was sequenced in the order of Cu > Ni > Pb > Cd > Ca, which followed the same order as the complexation stability constants between CPX and cations. The Fe-MCM-41 adsorbent possessed excellent reusability for 4 cycles use, suggesting a potential applicability of Fe-MCM-41 to remove CPX in water.

The Correlation of Adsorption Behavior between Ciprofloxacin Hydrochloride and the Active Sites of Fe-doped MCM-41

PubMed Central

Wu, Ying; Tang, Yiming; Li, Laisheng; Liu, Peihong; Li, Xukai; Chen, Weirui; Xue, Ying

2018-01-01

HIGHLIGHTS Fe incorporation significantly accelerated the adsorption of CPX on MCM-41.Fe leaching can be ignored when pH was higher than 4.0.pH played an important role in CPX adsorption on Fe-MCM-41.Co-effect of CPX and metal cations on Fe-MCM-41 was investigated. Fe-MCM-41s with various molar ratios of silicon to iron (20, 40, 80, and 160) were prepared to investigate adsorption properties of ciprofloxacin hydrochloride (CPX) in aqueous solutions. Fe-MCM-41s were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption isotherms, and infrared spectroscopy (FT-IR). Effects of silicon-iron ratio, adsorbent dosage, pH, and temperature were conducted to explore the adsorption mechanism of CPX on Fe-MCM-41. The results showed that the introduction of iron facilitated the absorption quantity for CPX from 20.04 to 83.33 mg g−1 at 120 min of reaction time, which was mainly attributed to surface complexation. The promotion of hydrophobic effect, electrostatic interactions, and π-π electron donor-acceptor interaction also played coordinate roles in the adsorption process. The experimental kinetic data followed both the pseudo-second-order and intra-particle diffusion models, while the adsorption isotherm data fit well to Freundlich model at high temperature. Thermodynamic study showed that the adsorption was spontaneous. Under the effect of electrostatic interaction, pH of the solution strongly affected CPX adsorption. Five representative metal cations (Ca, Cu, Ni, Pb, and Cd) were chosen to study the effects on CPX adsorption and their complexation. The inhibiting effect of metal cations on CPX adsorption was sequenced in the order of Cu > Ni > Pb > Cd > Ca, which followed the same order as the complexation stability constants between CPX and cations. The Fe-MCM-41 adsorbent possessed excellent reusability for 4 cycles use, suggesting a potential applicability of Fe-MCM-41 to remove CPX in water. PMID:29468153

Cu3-xP Nanocrystals as a Material Platform for Near-Infrared Plasmonics and Cation Exchange Reactions

PubMed Central

2015-01-01

Synthesis approaches to colloidal Cu3P nanocrystals (NCs) have been recently developed, and their optical absorption features in the near-infrared (NIR) have been interpreted as arising from a localized surface plasmon resonance (LSPR). Our pump–probe measurements on platelet-shaped Cu3-xP NCs corroborate the plasmonic character of this absorption. In accordance with studies on crystal structure analysis of Cu3P dating back to the 1970s, our density functional calculations indicate that this material is substoichiometric in copper, since the energy of formation of Cu vacancies in certain crystallographic sites is negative, that is, they are thermodynamically favored. Also, thermoelectric measurements point to a p-type behavior of the majority carriers from films of Cu3-xP NCs. It is likely that both the LSPR and the p-type character of our Cu3-xP NCs arise from the presence of a large number of Cu vacancies in such NCs. Motivated by the presence of Cu vacancies that facilitate the ion diffusion, we have additionally exploited Cu3-xP NCs as a starting material on which to probe cation exchange reactions. We demonstrate here that Cu3-xP NCs can be easily cation-exchanged to hexagonal wurtzite InP NCs, with preservation of the anion framework (the anion framework in Cu3-xP is very close to that of wurtzite InP). Intermediate steps in this reaction are represented by Cu3-xP/InP heterostructures, as a consequence of the fact that the exchange between Cu+ and In3+ ions starts from the peripheral corners of each NC and gradually evolves toward the center. The feasibility of this transformation makes Cu3-xP NCs an interesting material platform from which to access other metal phosphides by cation exchange. PMID:25960605

Application of the diffusive gradients in thin films technique for available potassium measurement in agricultural soils: effects of competing cations on potassium uptake by the resin gel.

PubMed

Zhang, Yulin; Mason, Sean; McNeill, Ann; McLaughlin, Michael J

2014-09-09

The utilization of Amberlite (IRP-69 ion-exchange resin, 100-500 wet mesh) as the binding phase in the diffusive gradients in thin films (DGT) technique has shown potential to improve the assessment of plant-available K in soils. The binding phase has recently been optimized by using a mixed Amberlite and ferrihydrite (MAF) gel which results in linear K uptake over extended deployment periods and in solutions with higher K concentrations. As restriction of K uptake by Ca on the Amberlite based resin gel has been previously proposed, potential competing effects of Ca(2+), Mg(2+) and NH(4+) on K uptake by the MAF gel were investigated. These cations had no effect on K elution efficiency which was 85%. However, K uptake by the MAF gel was restricted in the presence of competing cations in solution. Consequently, the diffusion coefficient of K decreased in the presence of cations compared to previous studies but was stable at 1.12×10(-5)cm(2)s(-1) at 25°C regardless of cation concentrations. Uptake of K by the DGT device was affected by the presence of excessive Ca in more than 30% of twenty typical Australian agricultural soils. However, this problem could be circumvented by using a shorter deployment time than the normal 24 h. Moderate correlation of concentrations of K extracted by DGT with Colwell K (extracted by NaHCO(3), R(2)=0.69) and NH4OAc K (R(2)=0.61) indicates that DGT measures a different pool of K in soils than that measured by the standard extractants used. In addition, the MAF gel has the ability to measure Ca and Mg simultaneously. Copyright © 2014 Elsevier B.V. All rights reserved.

The role of halide ions on the electrochemical behaviour of iron in alkali solutions

NASA Astrophysics Data System (ADS)

Begum, S. Nathira; Muralidharan, V. S.; Basha, C. Ahmed

2008-02-01

Active dissolution and passivation of transition metals in alkali solutions is of technological importance in batteries. The performance of alkaline batteries is decided by the presence of halides as they influence passivation. Cyclic voltammetric studies were carried out on iron in different sodium hydroxide solutions in presence of halides. In alkali solutions iron formed hydroxo complexes and their polymers in the interfacial diffusion layer. With progress of time they formed a cation selective layer. The diffusion layer turned into bipolar ion selective layer consisted of halides, a selective inner sublayer to the metal side and cation selective outer layer to the solution side. At very high anodic potentials, dehydration and deprotonation led to the conversion of salt layer into an oxide.

Solution of the nonlinear Poisson-Boltzmann equation: Application to ionic diffusion in cementitious materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arnold, J.; Kosson, D.S., E-mail: david.s.kosson@vanderbilt.edu; Garrabrants, A.

2013-02-15

A robust numerical solution of the nonlinear Poisson-Boltzmann equation for asymmetric polyelectrolyte solutions in discrete pore geometries is presented. Comparisons to the linearized approximation of the Poisson-Boltzmann equation reveal that the assumptions leading to linearization may not be appropriate for the electrochemical regime in many cementitious materials. Implications of the electric double layer on both partitioning of species and on diffusive release are discussed. The influence of the electric double layer on anion diffusion relative to cation diffusion is examined.

Natural zeolite reactivity towards ozone: the role of compensating cations.

PubMed

Valdés, Héctor; Alejandro, Serguei; Zaror, Claudio A

2012-08-15

Among indoor pollutants, ozone is recognised to pose a threat to human health. Recently, low cost natural zeolites have been applied as alternative materials for ozone abatement. In this work, the effect of compensating cation content of natural zeolite on ozone removal is studied. A Chilean natural zeolite is used here as starting material. The amount of compensating cations in the zeolite framework was modified by ion exchange using an ammonium sulphate solution (0.1 mol L(-1)). Characterisation of natural and modified zeolites were performed by X-ray powder diffraction (XRD), nitrogen adsorption at 77K, elemental analysis, X-ray fluorescence (XRF), thermogravimetric analysis coupled with mass spectroscopy (TGA-MS), and temperature-programmed desorption of ammonia (NH(3)-TPD). Ozone adsorption and/or decomposition on natural and modified zeolites were studied by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). Results show that the zeolite compensating cation content affects ozone interaction with zeolite active sites. Ammonium ion-exchange treatments followed by thermal out-gassing at 823 K, reduces ozone diffusion resistance inside the zeolite framework, increasing ozone abatement on zeolite surface active sites. Weak and strong Lewis acid sites of zeolite surface are identified here as the main active sites responsible of ozone removal. Copyright © 2012 Elsevier B.V. All rights reserved.

Nucleation and growth kinetics of electrodeposited sulfate-doped polypyrrole: determination of the diffusion coefficient of SO(4)(2-) in the polymeric membrane.

PubMed

Licona-Sánchez, T de J; Alvarez-Romero, G A; Mendoza-Huizar, L H; Galán-Vidal, C A; Palomar-Pardavé, M; Romero-Romo, M; Herrera-Hernández, H; Uruchurtu, J; Juárez-García, J M

2010-08-05

A kinetic study for the electrosynthesis of polypyrrole (Ppy) doped with SO(4)(2-) ions is presented. Ppy films were electrochemically polymerized onto a graphite-epoxy resin electrode. Experimental current density transients (j-t) were obtained for three different potentiometric behaviors: anionic, cationic, and a combination. Theoretical models were used to fit the experimental j-t data to determine the nucleation and growth processes controlling the polymer synthesis. It was encountered that, in all cases, pyrrole electropolimerization involves two concomitant processes, namely, a Ppy diffusion limited multiple 3D nucleation and growth and pyrrole electro-oxidation on the growing surface of the Ppy nuclei. SEM analysis of the electrodes surfaces reveals that Ppy deposition occurred over most of the electrode surface by multiple nucleation of hemispheres, as the theoretical model used for the analysis of the current transients required. Hemispherical particles formed the polymeric film displaying different sizes. The order for the particle size was as follows: anionic > anionic-cationic > cationic. These results are congruent with those obtained by theoretical analysis of the corresponding current transients. Analysis of the impedance measurements recorded on the anionic Ppy film, immersed in an aqueous solution with different sulfate ion concentrations evidenced that SO(4)(2-) ions diffuse through the Ppy film provoking a decrease of its electrical resistance and an increase of its dielectric constant. From the Warburg impedance coefficient, the sulfate coefficient of diffusion in the Ppy film was 1.38 x 10(-9) cm(2) s(-1).

In vivo cation exchange in quantum dots for tumor-specific imaging.

PubMed

Liu, Xiangyou; Braun, Gary B; Qin, Mingde; Ruoslahti, Erkki; Sugahara, Kazuki N

2017-08-24

In vivo tumor imaging with nanoprobes suffers from poor tumor specificity. Here, we introduce a nanosystem, which allows selective background quenching to gain exceptionally tumor-specific signals. The system uses near-infrared quantum dots and a membrane-impermeable etchant, which serves as a cation donor. The etchant rapidly quenches the quantum dots through cation exchange (ionic etching), and facilitates renal clearance of metal ions released from the quantum dots. The quantum dots are intravenously delivered into orthotopic breast and pancreas tumors in mice by using the tumor-penetrating iRGD peptide. Subsequent etching quenches excess quantum dots, leaving a highly tumor-specific signal provided by the intact quantum dots remaining in the extravascular tumor cells and fibroblasts. No toxicity is noted. The system also facilitates the detection of peritoneal tumors with high specificity upon intraperitoneal tumor targeting and selective etching of excess untargeted quantum dots. In vivo cation exchange may be a promising strategy to enhance specificity of tumor imaging.The imaging of tumors in vivo using nanoprobes has been challenging due to the lack of sufficient tumor specificity. Here, the authors develop a tumor-specific quantum dot system that permits in vivo cation exchange to achieve selective background quenching and high tumor-specific imaging.

Illitization of Potassium, Cesium, and Ammonium Exchanged Smectite

NASA Astrophysics Data System (ADS)

Mills, M. M.; Wang, Y.; Payne, C.; Sanchez, A. C.; Boisvert, L.; Matteo, E. N.

2017-12-01

Bentonite clay is a primary choice for engineered barrier systems within geologic repositories for disposal of radioactive wastes due to its low permeability at saturated states, warranting diffusion as the dominant transport mechanism, and large swelling pressures that promote sealing. In order to predict how well the barrier will function over time at repository relevant temperatures, it is important to understand thermal alteration effects on montmorillonite, better known as smectite, a main constituent of bentonite. One type of thermal alteration is the conversion to illite, when exposed to elevated temperatures and a sufficient amount of potassium ions, thereby weakening barrier functions. To facilitate the conversion of smectite to illite and examine the influence of interlayer cations, illitization experiments on cation exchanged smectite were performed within hydrothermal reaction vessels over one week timescales. The <2um fraction of a Na-rich smectite clay was first exchanged with 1M Cs, K, and NH4 salt solutions and further exposed to hydrous pyrolysis using a 1M KCl solution with various solid to liquid ratios at 200°C. Multiple analysis techniques were used to characterize the altered clay and identify extent of conversion, such as XRD, cation exchange capacity, and morphology changes by SEM. The pore-water chemistry was also analyzed by ICP-OES to detect any dissolved products and silica content. Results suggest the conversion rate is relatively fast, occurring within days, and is dependent on not only the amount of K, but also dissolved silica concentration related to total solid in solution. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia LLC, a wholly owned subsidiary of Honeywell International Inc. for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-NA0003525. SAND2017-7856A

The correlation of adsorption behavior between ciprofloxacin hydrochloride and the active sites of Fe-doped MCM-41

NASA Astrophysics Data System (ADS)

Wu, Ying; Tang, Yiming; Li, Laisheng; Liu, Peihong; Li, Xukai; Chen, Weirui; Xue, Ying

2018-02-01

Fe-MCM-41s with various molar ratios of silicon to iron (20, 40, 80 and 160) were prepared to investigate adsorption properties of ciprofloxacin hydrochloride (CPX) in aqueous solutions. Fe-MCM-41s were characterized by transmission electron microscope (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption/desorption isotherms and infrared spectroscopy (FT-IR). Effects of silicon–iron ratio, adsorbent dosage, pH and temperature were conducted to explore the adsorption mechanism of CPX on Fe-MCM-41. The results showed that the introduction of iron facilitated the absorption quantity for CPX from 20.04 to 83.33 mg g-1 at 120 min of reaction time, which was mainly attributed to surface complexation. The promotion of hydrophobic effect, electrostatic interactions and π-π electron donor–acceptor interaction also played coordinate roles in the adsorption process. The experimental kinetic data followed both the pseudo-second-order and intra-particle diffusion models, while the adsorption isotherm data fit well to Freundlich model at high temperature. Thermodynamic study showed that the adsorption was spontaneous. Under the effect of electrostatic interaction, pH of the solution strongly affected CPX adsorption. Five representative metal cations (Ca, Cu, Ni, Pb and Cd) were chosen to study the effects on CPX adsorption and their complexation. The inhibiting effect of metal cations on CPX adsorption was sequenced in the order of Cu > Ni > Pb > Cd > Ca, which followed the same order as the complexation stability constants between CPX and cations. The Fe-MCM-41 adsorbent possessed excellent reusability for 4 cycles use, suggesting a potential applicability of Fe-MCM-41 to remove CPX in water.

Reaction rates of oxygen with hemoglobin measured by non-equilibrium facilitated oxygen diffusion through hemoglobin solutions.

PubMed

Bouwer, S T; Hoofd, L; Kreuzer, F

2001-02-16

The purpose of this study was to verify the concept of non-equilibrium facilitated oxygen diffusion. This work succeeds our previous study, where facilitated oxygen diffusion by hemoglobin was measured at conditions of chemical equilibrium, and which yielded diffusion coefficients of hemoglobin and of oxygen. In the present work chemical non-equilibrium was induced using very thin diffusion layers. As a result, facilitation was decreased as predicted by theory. Thus, this work presents the first experimental demonstration of non-equilibrium facilitated oxygen diffusion. In addition, association and dissociation rate parameters of the reaction between oxygen and bovine and human hemoglobin were calculated and the effect of the homotropic and heterotropic interactions on each rate parameter was demonstrated. The results indicate that the homotropic interaction--which leads to increasing oxygen affinity with increasing oxygenation--is predominantly due to an increase in the association rate. The heterotropic interaction--which leads to decreasing oxygen affinity by anionic ligands--appears to be effected in two ways. Cl- increases the dissociation rate. In contrast, 2,3-diphosphoglycerate decreases the association rate.

Effect of Structure on Transport Properties (Viscosity, Ionic Conductivity, and Self-Diffusion Coefficient) of Aprotic Heterocyclic Anion (AHA) Room Temperature Ionic Liquids. 2. Variation of Alkyl Chain Length in the Phosphonium Cation.

PubMed

Sun, Liyuan; Morales-Collazo, Oscar; Xia, Han; Brennecke, Joan F

2016-06-30

A series of room-temperature ionic liquids (ILs) composed of triethyl(alkyl)phosphonium cations paired with three different aprotic heterocyclic anions (AHAs) (alkyl = butyl ([P2224](+)) and octyl ([P2228](+))) were prepared to investigate the effect of cationic alkyl chain length on transport properties. The transport properties and density of these ILs were measured from 283.15 to 343.15 K at ambient pressure. The dependence of the transport properties (viscosity, ionic conductivity, diffusivity, and molar conductivity) on temperature can be described by the Vogel-Fulcher-Tamman (VFT) equation. The ratio of the molar conductivity obtained from the molar concentration and ionic conductivity measurements to that calculated from self-diffusion coefficients (measured by pulsed gradient spin-echo nuclear magnetic resonance spectroscopy) using the Nernst-Einstein equation was used to quantify the ionicity of these ILs. The molar conductivity ratio decreases with increasing number of carbon atoms in the alkyl chain, indicating that the reduced Coulombic interactions resulting from lower density are more than balanced by the increased van der Waals interactions between the alkyl chains. The results of this study may provide insight into the design of ILs with enhanced dynamics that may be suitable as electrolytes in lithium ion batteries and other electrochemical applications.

Ion Transport and Structural Properties of Polymeric Electrolytes and Ionic Liquids from Molecular Dynamics Simulations

NASA Astrophysics Data System (ADS)

Borodin, Oleg

2010-03-01

Molecular dynamics simulations are well suited for exploring electrolyte structure and ion transport mechanisms on the nanometer length scale and the nanosecond time scales. In this presentation we will describe how MD simulations assist in answering fundamental questions about the lithium transport mechanisms in polymeric electrolytes and ionic liquids. In particular, in the first part of the presentation the extent of ion aggregation, the structure of ion aggregates and the lithium cation diffusion in binary polymeric electrolytes will be compared with that of single-ion conducting polymers. In the second part of the talk, the lithium transport in polymeric electrolytes will be compared with that of three ionic liquids ( [emim][FSI] doped with LiFSI , [pyr13][FSI] doped with LiFSI, [emim][BF4] doped with LiBF4). The relation between ionic liquid self-diffusion, conductivity and thermodynamic properties will be discussed in details. A number of correlations between heat of vaporization Hvap, cation-anion binding energy (E+/-), molar volume (Vm), self-diffusion coefficient (D) and ionic conductivity for 29 ionic liquids have been investigated using MD simulations. A significant correlation between D and Hvap has been found, while best correlation was found for -log((D Vm)) vs. Hvap+0.28E+/-. A combination of enthalpy of vaporization and a fraction of the cation-anion binding energy was suggested as a measure of the effective cohesive energy for ionic liquids.

Protonation switching to the least-basic heteroatom of carbamate through cationic hydrogen bonding promotes the formation of isocyanate cations.

PubMed

Kurouchi, Hiroaki; Sumita, Akinari; Otani, Yuko; Ohwada, Tomohiko

2014-07-07

We found that phenethylcarbamates that bear ortho-salicylate as an ether group (carbamoyl salicylates) dramatically accelerate OC bond dissociation in strong acid to facilitate generation of isocyanate cation (N-protonated isocyanates), which undergo subsequent intramolecular aromatic electrophilic cyclization to give dihydroisoquinolones. To generate isocyanate cations from carbamates in acidic media as electrophiles for aromatic substitution, protonation at the ether oxygen, the least basic heteroatom, is essential to promote CO bond cleavage. However, the carbonyl oxygen of carbamates, the most basic site, is protonated exclusively in strong acids. We found that the protonation site can be shifted to an alternative basic atom by linking methyl salicylate to the ether oxygen of carbamate. The methyl ester oxygen ortho to the phenolic (ether) oxygen of salicylate is as basic as the carbamate carbonyl oxygen, and we found that monoprotonation at the methyl ester oxygen in strong acid resulted in the formation of an intramolecular cationic hydrogen bond (>CO(+) H⋅⋅⋅O<) with the phenolic ether oxygen. This facilitates OC bond dissociation of phenethylcarbamates, thereby promoting isocyanate cation formation. In contrast, superacid-mediated diprotonation at the methyl ester oxygen of the salicylate and the carbonyl oxygen of the carbamate afforded a rather stable dication, which did not readily undergo CO bond dissociation. This is an unprecedented and unknown case in which the monocation has greater reactivity than the dication. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Size and Charge Dependence of Ion Transport in Human Nail Plate

PubMed Central

Baswan, Sudhir M.; Li, S. Kevin; LaCount, Terri D.; Kasting, Gerald B.

2016-01-01

The electrical properties of human nail plate are poorly characterized, yet are a key determinate of the potential to treat nail diseases such as onychomycosis using iontophoresis. In order to address this deficiency, molar conductivities of 17 electrolytes comprising 12 ionic species were determined in hydrated human nail plate in vitro. Cation transport numbers across the nail for 11 of these electrolytes were determined by the electromotive force method. Effective ionic mobilities and diffusivities at infinite dilution for all ionic species were determined by regression analysis. The ratios of diffusivities in nail to those in solution were found to correlate inversely with the hydrodynamic radii of the ions according to a power law relationship having an exponent of −1.75 ± 0.27, a substantially steeper size dependence than observed for similar experiments in skin. Effective diffusivities of cations in nail were three-fold higher than those of comparably sized anions. These results reflect the strong size and charge selectivity of the nail plate for ionic conduction and diffusion. The analysis implies that efficient transungual iontophoretic delivery of ionized drugs having radii upwards of 5 Å (approximately MW ≥ 340 Da) will require chemical or mechanical alteration of the nail plate. PMID:26886342

Effect of low frequency, low amplitude magnetic fields on the permeability of cationic liposomes entrapping carbonic anhydrase: I. Evidence for charged lipid involvement.

PubMed

Ramundo-Orlando, A; Morbiducci, U; Mossa, G; D'Inzeo, G

2000-10-01

The influence of low frequency (4-16 Hz), low amplitude (25-75 mu T) magnetic fields on the diffusion processes in enzyme-loaded unilamellar liposomes as bioreactors was studied. Cationic liposomes containing dipalmitoylphosphatidylcholine, cholesterol, and charged lipid stearylamine (SA) at different molar ratios (6:3:1 or 5:3:2) were used. Previous kinetic experiments showed a very low self-diffusion rate of the substrate p-nitrophenyl acetate (p-NPA) across intact liposome bilayer. After 60 min of exposure to 7 Hz sinusoidal (50 mu T peak) and parallel static (50 mu T) magnetic fields the enzyme activity, as a function of increased diffusion rate of p-NPA, rose from 17 +/- 3% to 80 +/- 9% (P < .0005, n = 15) in the 5:3:2 liposomes. This effect was dependent on the SA concentration in the liposomes. Only the presence of combined sinusoidal (AC) and static (DC) magnetic fields affected the p-NPA diffusion rates. No enzyme leakage was observed. Such studies suggest a plausible link between the action of extremely low frequency magnetic field on charged lipids and a change of membrane permeability. Copyright 2000 Wiley-Liss, Inc.

Static and transport properties of alkyltrimethylammonium cation-based room-temperature ionic liquids.

PubMed

Seki, Shiro; Tsuzuki, Seiji; Hayamizu, Kikuko; Serizawa, Nobuyuki; Ono, Shimpei; Takei, Katsuhito; Doi, Hiroyuki; Umebayashi, Yasuhiro

2014-05-01

We have measured physicochemical properties of five alkyltrimethylammonium cation-based room-temperature ionic liquids and compared them with those obtained from computational methods. We have found that static properties (density and refractive index) and transport properties (ionic conductivity, self-diffusion coefficient, and viscosity) of these ionic liquids show close relations with the length of the alkyl chain. In particular, static properties obtained by experimental methods exhibit a trend complementary to that by computational methods (refractive index ∝ [polarizability/molar volume]). Moreover, the self-diffusion coefficient obtained by molecular dynamics (MD) simulation was consistent with the data obtained by the pulsed-gradient spin-echo nuclear magnetic resonance technique, which suggests that computational methods can be supplemental tools to predict physicochemical properties of room-temperature ionic liquids.

Ion-Migration Inhibition by the Cation-π Interaction in Perovskite Materials for Efficient and Stable Perovskite Solar Cells.

PubMed

Wei, Dong; Ma, Fusheng; Wang, Rui; Dou, Shangyi; Cui, Peng; Huang, Hao; Ji, Jun; Jia, Endong; Jia, Xiaojie; Sajid, Sajid; Elseman, Ahmed Mourtada; Chu, Lihua; Li, Yingfeng; Jiang, Bing; Qiao, Juan; Yuan, Yongbo; Li, Meicheng

2018-06-25

Migration of ions can lead to photoinduced phase separation, degradation, and current-voltage hysteresis in perovskite solar cells (PSCs), and has become a serious drawback for the organic-inorganic hybrid perovskite materials (OIPs). Here, the inhibition of ion migration is realized by the supramolecular cation-π interaction between aromatic rubrene and organic cations in OIPs. The energy of the cation-π interaction between rubrene and perovskite is found to be as strong as 1.5 eV, which is enough to immobilize the organic cations in OIPs; this will thus will lead to the obvious reduction of defects in perovskite films and outstanding stability in devices. By employing the cation-immobilized OIPs to fabricate perovskite solar cells (PSCs), a champion efficiency of 20.86% and certified efficiency of 20.80% with negligible hysteresis are acquired. In addition, the long-term stability of cation-immobilized PSCs is improved definitely (98% of the initial efficiency after 720 h operation), which is assigned to the inhibition of ionic diffusions in cation-immobilized OIPs. This cation-π interaction between cations and the supramolecular π system enhances the stability and the performance of PSCs efficiently and would be a potential universal approach to get the more stable perovskite devices. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Atomistic understanding of cation exchange in PbS nanocrystals using simulations with pseudoligands

PubMed Central

Fan, Zhaochuan; Lin, Li-Chiang; Buijs, Wim; Vlugt, Thijs J. H.; van Huis, Marijn A.

2016-01-01

Cation exchange is a powerful tool for the synthesis of nanostructures such as core–shell nanocrystals, however, the underlying mechanism is poorly understood. Interactions of cations with ligands and solvent molecules are systematically ignored in simulations. Here, we introduce the concept of pseudoligands to incorporate cation-ligand-solvent interactions in molecular dynamics. This leads to excellent agreement with experimental data on cation exchange of PbS nanocrystals, whereby Pb ions are partially replaced by Cd ions from solution. The temperature and the ligand-type control the exchange rate and equilibrium composition of cations in the nanocrystal. Our simulations reveal that Pb ions are kicked out by exchanged Cd interstitials and migrate through interstitial sites, aided by local relaxations at core–shell interfaces and point defects. We also predict that high-pressure conditions facilitate strongly enhanced cation exchange reactions at elevated temperatures. Our approach is easily extendable to other semiconductor compounds and to other families of nanocrystals. PMID:27160371

Rotational diffusion of nonpolar and ionic solutes in 1-alkyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imides: is solute rotation always influenced by the length of the alkyl chain on the imidazolium cation?

PubMed

Gangamallaiah, V; Dutt, G B

2012-10-25

In an attempt to find out whether the length of the alkyl chain on the imidazolium cation has a bearing on solute rotation, temperature-dependent fluorescence anisotropies of three structurally similar solutes have been measured in a series of 1-alkyl-3-methylimidazolium (alkyl = methyl, ethyl, propyl, butyl, and hexyl) bis(trifluoromethylsulfonyl)imides. Solute-solvent coupling constants obtained from the experimentally measured reorientation times with the aid of Stokes-Einstein-Debye hydrodynamic theory indicate that there is no influence of the length of the alkyl chain on the rotation of nonpolar, anionic, and cationic solutes 9-phenylanthracene (9-PA), fluorescein (FL), and rhodamine 110 (R110), respectively. It has also been noticed that the rotational diffusion of 9-PA is closer to the predictions of slip hydrodynamics, whereas the rotation of negatively charged FL and positively charged R110 is almost identical and follows stick hydrodynamics in these ionic liquids. Despite having similar shape and size, ionic solutes rotate slower by a factor of 3-4 compared to the nonpolar solute. Interplay of specific and electrostatic interactions between FL and the imidazolium cation of the ionic liquids, and between R110 and the bis(trifluoromethylsulfonyl)imide anion, appear to be responsible for the observed behavior. These results are an indication that the length of the alkyl chain on the imidazolium cation does not alter their physical properties in a manner that has an effect on solute rotation.

The Role of Dopant Ions on Charge Injection and Transport in Electrochemically Doped Quantum Dot Films.

PubMed

Gudjonsdottir, Solrun; van der Stam, Ward; Kirkwood, Nicholas; Evers, Wiel H; Houtepen, Arjan J

2018-05-16

Control over the charge density is very important for implementation of colloidal semiconductor nanocrystals into various optoelectronic applications. A promising approach to dope nanocrystal assemblies is charge injection by electrochemistry, in which the charge compensating electrolyte ions can be regarded as external dopant ions. To gain insight into the doping mechanism and the role of the external dopant ions, we investigate charge injection in ZnO nanocrystal assemblies for a large series of charge compensating electrolyte ions with spectroelectrochemical and electrochemical transistor measurements. We show that charge injection is limited by the diffusion of cations in the nanocrystal films as their diffusion coefficient are found to be ∼7 orders of magnitude lower than those of electrons. We further show that the rate of charge injection depends strongly on the cation size and cation concentration. Strikingly, the onset of electron injection varies up to 0.4 V, depending on the size of the electrolyte cation. For the small ions Li + and Na + the onset is at significantly less negative potentials. For larger ions (K + , quaternary ammonium ions) the onset is always at the same, more negative potential, suggesting that intercalation may take place for Li + and Na + . Finally, we show that the nature of the charge compensating cation does not affect the source-drain electronic conductivity and mobility, indicating that shallow donor levels from intercalating ions fully hybridize with the quantum confined energy levels and that the reorganization energy due to intercalating ions does not strongly affect electron transport in these nanocrystal assemblies.

The Role of Dopant Ions on Charge Injection and Transport in Electrochemically Doped Quantum Dot Films

PubMed Central

2018-01-01

Control over the charge density is very important for implementation of colloidal semiconductor nanocrystals into various optoelectronic applications. A promising approach to dope nanocrystal assemblies is charge injection by electrochemistry, in which the charge compensating electrolyte ions can be regarded as external dopant ions. To gain insight into the doping mechanism and the role of the external dopant ions, we investigate charge injection in ZnO nanocrystal assemblies for a large series of charge compensating electrolyte ions with spectroelectrochemical and electrochemical transistor measurements. We show that charge injection is limited by the diffusion of cations in the nanocrystal films as their diffusion coefficient are found to be ∼7 orders of magnitude lower than those of electrons. We further show that the rate of charge injection depends strongly on the cation size and cation concentration. Strikingly, the onset of electron injection varies up to 0.4 V, depending on the size of the electrolyte cation. For the small ions Li+ and Na+ the onset is at significantly less negative potentials. For larger ions (K+, quaternary ammonium ions) the onset is always at the same, more negative potential, suggesting that intercalation may take place for Li+ and Na+. Finally, we show that the nature of the charge compensating cation does not affect the source-drain electronic conductivity and mobility, indicating that shallow donor levels from intercalating ions fully hybridize with the quantum confined energy levels and that the reorganization energy due to intercalating ions does not strongly affect electron transport in these nanocrystal assemblies. PMID:29718666

Polymorphic phase transitions and molecular motion in pyridinium chlorochromate

NASA Astrophysics Data System (ADS)

Pajaķ, Z.; Szafrańska, B.; Czarnecki, P.; Mayer, J.; Kozak, A.

1997-08-01

DTA, DSC, NMR and dielectric studies have been performed for pyridinium chlorochromate over a wide temperature range. A sequence of four solid-solid phase transitions was discovered. The in-plane complex reorientation of the cation is described by a three-well potential model with two correlation times. At higher temperatures one observes simultaneous cation tumbling and diffusion. Thus existence of a new ionic plastic phase is revealed. The domain structure observed suggests ferroelastic properties of the compound.

Predicting Salt Permeability Coefficients in Highly Swollen, Highly Charged Ion Exchange Membranes.

PubMed

Kamcev, Jovan; Paul, Donald R; Manning, Gerald S; Freeman, Benny D

2017-02-01

This study presents a framework for predicting salt permeability coefficients in ion exchange membranes in contact with an aqueous salt solution. The model, based on the solution-diffusion mechanism, was tested using experimental salt permeability data for a series of commercial ion exchange membranes. Equilibrium salt partition coefficients were calculated using a thermodynamic framework (i.e., Donnan theory), incorporating Manning's counterion condensation theory to calculate ion activity coefficients in the membrane phase and the Pitzer model to calculate ion activity coefficients in the solution phase. The model predicted NaCl partition coefficients in a cation exchange membrane and two anion exchange membranes, as well as MgCl 2 partition coefficients in a cation exchange membrane, remarkably well at higher external salt concentrations (>0.1 M) and reasonably well at lower external salt concentrations (<0.1 M) with no adjustable parameters. Membrane ion diffusion coefficients were calculated using a combination of the Mackie and Meares model, which assumes ion diffusion in water-swollen polymers is affected by a tortuosity factor, and a model developed by Manning to account for electrostatic effects. Agreement between experimental and predicted salt diffusion coefficients was good with no adjustable parameters. Calculated salt partition and diffusion coefficients were combined within the framework of the solution-diffusion model to predict salt permeability coefficients. Agreement between model and experimental data was remarkably good. Additionally, a simplified version of the model was used to elucidate connections between membrane structure (e.g., fixed charge group concentration) and salt transport properties.

Electronic absorption spectra of hydrogenated protonated naphthalene and proflavine

NASA Astrophysics Data System (ADS)

Bonaca, A.; Bilalbegović, G.

2011-09-01

We study hydrogenated cations of two polycyclic hydrocarbon molecules as models of hydrogenated organic species that form in the interstellar medium. Optical spectra of the hydrogenated naphthalene cation Hn-C10H+8 for n= 1, 2 and 10, as well as the astrobiologically interesting hydrogenated proflavine cation Hn-C13H11N+3 for n= 1 and 14, are calculated. The pseudopotential time-dependent density functional theory is used. It is found that the fully hydrogenated proflavine cation H14-C13H11N+3 shows a broad spectrum in which the positions of individual lines are almost lost. The positions, shapes and intensities of lines change in hydronaphthalene and hydroproflavine cations, showing that hydrogen additions induce substantially different optical spectra in comparison with base polycyclic hydrocarbon cations. One calculated line in the visible spectrum of H10-C10H+8 and one in the visible spectrum of H-C13H11N+3 are close to the measured diffuse interstellar bands. We also present the positions of near-ultraviolet lines.

Polarizability effects on the structure and dynamics of ionic liquids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cavalcante, Ary de Oliveira, E-mail: arycavalcante@ufam.edu.br; Departamento de Química, Universidade Federal do Amazonas, Av. Rodrigo Octávio, 6200, Coroado, Manaus, AM; Ribeiro, Mauro C. C.

2014-04-14

Polarization effects on the structure and dynamics of ionic liquids are investigated using molecular dynamics simulations. Four different ionic liquids were simulated, formed by the anions Cl{sup −} and PF{sub 6}{sup −}, treated as single fixed charge sites, and the 1-n-alkyl-3-methylimidazolium cations (1-ethyl and 1-butyl-), which are polarizable. The partial charge fluctuation of the cations is provided by the electronegativity equalization model (EEM) and a complete parameter set for the cations electronegativity (χ) and hardness (J) is presented. Results obtained from a non-polarizable model for the cations are also reported for comparison. Relative to the fixed charged model, the equilibriummore » structure of the first solvation shell around the imidazolium cations shows that inclusion of EEM polarization forces brings cations closer to each other and that anions are preferentially distributed above and below the plane of the imidazolium ring. The polarizable model yields faster translational and reorientational dynamics than the fixed charges model in the rotational-diffusion regime. In this sense, the polarizable model dynamics is in better agreement with the experimental data.« less

Trace element diffusion and kinetic fractionation in wet rhyolitic melt

NASA Astrophysics Data System (ADS)

Holycross, Megan E.; Watson, E. Bruce

2018-07-01

Piston-cylinder experiments were run to determine the chemical diffusivities of 21 trace elements (Sc, V, Y, Zr, Nb, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Hf, Th and U) in hydrous rhyolitic melts at 1 GPa pressure and temperatures from 850 to 1250 °C. Diffusion couple glasses were doped with trace elements in low concentrations to characterize the diffusivities of all cations in a single experiment. Laser ablation ICP-MS was used to evaluate the trace element concentration gradients that developed in the silicate glasses. All calculated diffusion coefficients correspond to the temperature dependence D = D0exp(-Ea/RT). Rhyolite liquids contained either ∼4.1 wt% or ∼6.2 wt% dissolved H2O; separate Arrhenius relationships are produced for each melt composition. Trace element diffusivities in the melt with 6.2 wt% H2O are roughly two times higher than those in the less hydrous melt. Calculated trace element diffusion coefficients cover nearly two orders of magnitude at a given temperature. The high field strength elements are the slowest diffusers, followed by the transition metals and heavy rare earth elements. The light rare earth elements have the fastest diffusion rates in hydrous rhyolitic melt. The measured diffusion coefficients range down to values sufficiently low to preclude diffusive homogenization over geochemically realistic time scales in some cases. The substantial differences in the diffusivities of individual cations may result in fractionated trace element signatures in rhyolite melt pockets. A simple model is used to explore the potential for kinetic fractionation of REE during growth of an apatite crystal in a diffusive boundary layer locally saturated in P2O5. The faster-diffusing light REE are more efficiently transported away from the crystal interface than the slower-moving heavy REE. Diffusion effects will enrich the melt boundary layer in slow-moving HREE relative to the faster LREE. The kinetic fractionation of REE in the melt growth medium will result in a precipitated apatite crystal with a disequilibrium trace element composition.

LiBi{sub 3}S{sub 5}—A lithium bismuth sulfide with strong cation disorder

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nakhal, Suliman; Wiedemann, Dennis, E-mail: dennis.wiedemann@chem.tu-berlin.de; Stanje, Bernhard

Among chalcogenide semiconductors for thermoelectric applications, alkali-metal bismuth compounds occur in many complex compositions favorable for high performance. Although LiBi{sub 3}S{sub 5} had been announced in 1977, the potential 1D lithium-ion conductor has hitherto eluded selective synthesis and structure determination. In this study, we present a solid-state route to phase-pure LiBi{sub 3}S{sub 5} powder starting from LiBiS{sub 2} and Bi{sub 2}S{sub 3}. Neutron diffractograms and lithium NMR spectra reveal its crystal structure to be a cation-disordered variety of the AgBi{sub 3}S{sub 5} type (synthetic pavonite; monoclinic, C2/m). Topological analyses and lithium NMR relaxometry suggest that correlated lithium-ion diffusion with activationmore » energies up to 0.66(2) eV occurs along the channels in b direction including tetrahedral voids. Because of cation disorder, immobile bismuth(III) ions clog these pathways, making LiBi{sub 3}S{sub 5} a moderate to poor ionic conductor. The synthesis route reported is nonetheless promising for new lithium bismuth sulfides with, possibly ordered, structure types of the pavonite homologous series. - Graphical abstract: Phase-pure LiBi{sub 3}S{sub 5} has been synthesized and shown to crystallize in cation-disordered variety of the AgBi{sub 3}S{sub 5} type (synthetic pavonite, C2/m) using neutron diffractometry. Topological analyses and NMR relaxometry suggest that immobile Bi{sup 3+} ions clog migration channels along b, making the material a poor lithium conductor. Display Omitted - Highlights: • Phase-pure LiBi{sub 3}S{sub 5} has been synthesized using a promising solid-state route. • LiBi{sub 3}S{sub 5} crystallizes in a cation-disordered variant of the AgBi{sub 3}S{sub 5} type. • Topological analyses suggest lithium diffusion in channels along b. • NMR relaxometry finds activation energies of diffusion as high as 0.66(2) eV. • Because of disorder, LiBi{sub 3}S{sub 5} is a moderate to poor lithium-ion conductor.« less

Computation Of Facilitated Transport of O2 In Hemoglobin

NASA Technical Reports Server (NTRS)

Davis, Sanford

1991-01-01

Report describes computations of unsteady facilitated transport of oxygen through liquid membrane of hemoglobin. Used here, "facilitated transport" means diffusion of permeant through membrane in which that diffusion enhanced by reversible chemical reaction between permeant and membrane. In this case, reversible reactions between hemoglobin and oxygen.

Variable Temperature Infrared Spectroscopy Investigation of Benzoic Acid Interactions with Montmorillonite Clay Interlayer Water.

PubMed

Nickels, Tara M; Ingram, Audrey L; Maraoulaite, Dalia K; White, Robert L

2015-07-01

Molecular interactions between benzoic acid and cations and water contained in montmorillonite clay interlayer spaces are characterized by using variable temperature diffuse reflection infrared Fourier transform spectroscopy (VT-DRIFTS). Using sample perturbation and difference spectroscopy, infrared spectral changes resulting from removal of interlayer water and associated changes in local benzoic acid environments are identified. Difference spectra features can be correlated with changes in specific molecular vibrations that are characteristic of benzoic acid molecular orientation. Results suggest that the carboxylic acid functionality of benzoic acid interacts with interlayer cations through a bridging water molecule and that this interaction is affected by the nature of the cation present in the clay interlayer space.

Methods and apparatus for using gas and liquid phase cathodic depolarizers

NASA Technical Reports Server (NTRS)

Murphy, Oliver J. (Inventor); Hitchens, G. Duncan (Inventor)

1998-01-01

The invention provides methods for using gas and liquid phase cathodic depolarizers in an electrochemical cell having a cation exchange membrane in intimate contact with the anode and cathode. The electrochemical conversion of cathodic depolarizers at the cathode lowers the cell potential necessary to achieve a desired electrochemical conversion, such as ozone evolution, at the anode. When gaseous cathodic depolarizers, such as oxygen, are used, a gas diffusion cathode having the cation exchange membrane bonded thereto is preferred. When liquid phase cathodic depolarizers are used, the cathode may be a flow-by electrode, flow-through electrode, packed-bed electrode or a fluidized-bed electrode in intimate contact with the cation exchange membrane.

Water vapor diffusion membrane development. [for water recovery purposes onboard manned spacecraft

NASA Technical Reports Server (NTRS)

Tan, M. K.

1974-01-01

The phase separator component used as a membrane in the vapor diffusion process (VRD) for the recovery of potable water from urine on manned space missions of extended duration was investigated, with particular emphasis on cation-selective membranes because of their noted mechanical strength, superior resistance to acids, oxidants, and germicides, and their potential resistance to organic foulants. Two of the membranes were tested for 700 hours continuously, and were selected on the basis of criteria deemed important to an effective water reclamation system onboard spacecraft. The samples of urine were successfully processed by removing 93 percent of their water content in 70 hours using the selected membranes. Pretreatment with an acid-oxidant formulation improved product quality. Cation exchange membranes were shown to possess superior mechanical strength and chemical resistance, as compared to cellulosic membranes.

Proton transport by phosphate diffusion--a mechanism of facilitated CO2 transfer

PubMed Central

1976-01-01

We have measured CO2 fluxes across phosphate solutions at different carbonic anhydrase concentrations, bicarbonate concentration gradients, phosphate concentrations, and mobilities. Temperature was 22-25 degrees C, the pH of the phosphate solutions was 7.0-7.3. We found that under physiological conditions of pH and pCO2 a facilitated diffusion of CO2 occurs in addition to free diffusion when (a) sufficient carbonic anhydrase is present, and (b) a concentration gradient of HCO3- is established along with a pCO2 gradient, and (c) the phosphate buffer has a mobility comparable to that of bicarbonate. When the phosphate was immobilized by attaching 0.25-mm-long cellulose particles, no facilitation of CO2 diffusion was detectable. A mechanism of facilitated CO2 diffusion in phosphate solutions analogous to that in albumin solutions was proposed on the basis of these findings: bicarbonate diffusion together with a facilitated proton transport by phosphate diffusion. A mathematical model of this mechanism was formulated. The CO2 fluxed predicted by the model agree quantitatively with the experimentally determined fluxes. It is concluded that a highly effective proton transport mechanism acts in solutions of mobile phosphate buffers. By this mechanism; CO2 transfer may be increased up to fivefold and proton transfer may be increased to 10,000-fold. PMID:6619

Biphasic interactions between a cationic dendrimer and actin.

PubMed

Ruenraroengsak, Pakatip; Florence, Alexander T

2010-12-01

Gene delivery systems face the problem not only of the route toward the cell and tissues in question, but also of the molecularly crowded environment of both the cytoplasm and the nucleus itself. One of the physical barriers in the cytoplasm for diffusing nanoparticles is an actin network. Here, we describe the finding that a self-fluorescent sixth generation cationic dendrimer (6 nm in diameter) interacts reversibly and possibly electrostatically with actin filaments in vitro. Not only does this interaction slow the diffusion of the dendrimer but it also affects actin polymerization in a biphasic manner. At low concentrations the dendrimer behaves like a G-binding actin protein, retarding actin polymerization, whereas at high concentrations the dendrimer acts as a nucleating protein accelerating the polymerization. Thus in vivo the diffusion of a dendrimer carrier such as this has both physical and chemical elements: by decreasing polymerization it might accelerate its own transport, and by enhancing actin polymerization retard it. This finding suggests that such a dendrimer may have a role as an anticancer agent through its inhibitory effect on actin polymerization.

Simultaneous Extraction of Lithium and Hydrogen from Seawater

DTIC Science & Technology

2011-08-22

to the anode and cathode were determined by ion chromatography . Anions were analyzed by Anion Ion Chromatography (Instrument Dionex ICS-1500, Column...and oxygen gases coming out of the cell were collected and the amount was measured volumetrically. Ion chromatography : Ions in seawater diffused from... Dionex AS9-HC; AG9-HC Guard, eluent: 9.00 mM Na2CO3, flow rate: 1.25 mL/min, and sample loop was 25 μL). Cations were analyzed by Cation Ion

The rate of the deoxygenation reaction limits myoglobin- and hemoglobin-facilitated O₂ diffusion in cells.

PubMed

Endeward, Volker

2012-05-01

A mathematical model describing facilitation of O(2) diffusion by the diffusion of myoglobin and hemoglobin is presented. The equations are solved numerically by a finite-difference method for the conditions as they prevail in cardiac and skeletal muscle and in red cells without major simplifications. It is demonstrated that, in the range of intracellular diffusion distances, the degree of facilitation is limited by the rate of the chemical reaction between myglobin or hemoglobin and O(2). The results are presented in the form of relationships between the degree of facilitation and the length of the diffusion path on the basis of the known kinetics of the oxygenation-deoxygenation reactions. It is concluded that the limitation by reaction kinetics reduces the maximally possible facilitated oxygen diffusion in cardiomyoctes by ∼50% and in skeletal muscle fibers by ∼ 20%. For human red blood cells, a reduction of facilitated O(2) diffusion by 36% is obtained in agreement with previous reports. This indicates that, especially in cardiomyocytes and red cells, chemical equilibrium between myoglobin or hemoglobin and O(2) is far from being established, an assumption that previously has often been made. Although the "O(2) transport function" of myoglobin in cardiac muscle cells thus is severely limited by the chemical reaction kinetics, and to a lesser extent also in skeletal muscle, it is noteworthy that the speed of release of O(2) from MbO(2), the "storage function," is not limited by the reaction kinetics under physiological conditions.

Cation Diffusion in Plagioclase Feldspar

NASA Astrophysics Data System (ADS)

Morse, S. A.

1984-08-01

Steep compositional gradients in igneous plagioclase feldspar from slowly cooled intrusive bodies imply a maximum value of the intracrystalline diffusion coefficient for NaSi leftrightarrows CaAl exchange, Dmax~ 10-20 centimeters squared per second for temperatures in the range 1250 degrees to 1000 degrees C. Millimeter-sized grains cannot be homogenized in all geologic time; hence reactive equilibrium crystallization of plagioclase from the melt does not occur in dry systems.

Size and Charge Dependence of Ion Transport in Human Nail Plate.

PubMed

Baswan, Sudhir M; Li, S Kevin; LaCount, Terri D; Kasting, Gerald B

2016-03-01

The electrical properties of human nail plate are poorly characterized yet are a key determinate of the potential to treat nail diseases, such as onychomycosis, using iontophoresis. To address this deficiency, molar conductivities of 17 electrolytes comprising 12 ionic species were determined in hydrated human nail plate in vitro. Cation transport numbers across the nail for 11 of these electrolytes were determined by the electromotive force method. Effective ionic mobilities and diffusivities at infinite dilution for all ionic species were determined by regression analysis. The ratios of diffusivities in nail to those in solution were found to correlate inversely with the hydrodynamic radii of the ions according to a power law relationship having an exponent of -1.75 ± 0.27, a substantially steeper size dependence than observed for similar experiments in skin. Effective diffusivities of cations in nail were 3-fold higher than those of comparably sized anions. These results reflect the strong size and charge selectivity of the nail plate for ionic conduction and diffusion. The analysis implies that efficient transungual iontophoretic delivery of ionized drugs having radii upward of 5 Å (molecular weight, ca. ≥ 340 Da) will require chemical or mechanical alteration of the nail plate. Copyright © 2016 American Pharmacists Association®. Published by Elsevier Inc. All rights reserved.

Ionic and electronic behaviors of earth-abundant semiconductor materials and their applications toward solar energy harvesting

NASA Astrophysics Data System (ADS)

Mayer, Matthew T.

Semiconductor devices offer promise for efficient conversion of sunlight into other useful forms of energy, in either photovoltaic or photoelectrochemical cell configurations to produce electrical power or chemical energy, respectively. This dissertation examines ionic and electronic phenomena in some candidate semiconductors and seeks to understand their implications toward solar energy conversion applications. First, copper sulfide (Cu2S) was examined as a candidate photovoltaic material. It was discovered that its unique property of cation diffusion allows the room-temperature synthesis of vertically-aligned nanowire arrays, a morphology which facilitates study of the diffusion processes. This diffusivity was found to induce hysteresis in the electronic behavior, leading to the phenomena of resistive switching and negative differential resistance. The Cu2S were then demonstrated as morphological templates for solid-state conversion into different types of heterostructures, including segmented and rod-in-tube morphologies. Near-complete conversion to ZnS, enabled by the out-diffusion of Cu back into the substrate, was also achieved. While the ion diffusion property likely hinders the reliability of Cu 2S in photovoltaic applications, it was shown to enable useful electronic and ionic behaviors. Secondly, iron oxide (Fe2O3, hematite) was examined as a photoanode for photoelectrochemical water splitting. Its energetic limitations toward the water electrolysis reactions were addressed using two approaches aimed at achieving greater photovoltages and thereby improved water splitting efficiencies. In the first, a built-in n-p junction produced an internal field to drive charge separation and generate photovoltage. In the second, Fe 2O3 was deposited onto a smaller band gap material, silicon, to form a device capable of producing enhanced total photovoltage by a dual-absorber Z-scheme mechanism. Both approaches resulted in a cathodic shift of the photocurrent onset potential, signifying enhanced power output and progress toward the unassisted photoelectrolysis of water.

Sticky when wet

NASA Astrophysics Data System (ADS)

Chen, Ji; Michaelides, Angelos

2018-03-01

The aqueous hydronium cation diffuses about twice as fast as the aqueous hydroxide anion in liquid water, but the origin of this behaviour has been unclear. Now, state-of-the-art simulations provide an explanation for this long-standing conundrum.

Tunable electrical conductivity in oriented thin films of tetrathiafulvalene-based covalent organic framework

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cai, SL; Zhang, YB; Pun, AB

2014-09-16

Despite the high charge-carrier mobility in covalent organic frameworks (COFs), the low intrinsic conductivity and poor solution processability still impose a great challenge for their applications in flexible electronics. We report the growth of oriented thin films of a tetrathiafulvalene-based COF (TTF-COF) and its tunable doping. The porous structure of the crystalline TTF-COF thin film allows the diffusion of dopants such as I-2 and tetracyanoquinodimethane (TCNQ) for redox reactions, while the closely packed 2D grid sheets facilitate the cross-layer delocalization of thus-formed TTF radical cations to generate more conductive mixed-valence TTF species, as is verified by UV-vis-NIR and electron paramagneticmore » resonance spectra. Conductivity as high as 0.28 S m(-1) is observed for the doped COF thin films, which is three orders of magnitude higher than that of the pristine film and is among the highest for COF materials.« less

Molecular understanding of polyelectrolyte binders that actively regulate ion transport in sulfur cathodes

DOE PAGES

Li, Longjun; Pascal, Tod A.; Connell, Justin G.; ...

2017-12-22

Polymer binders in battery electrodes may be either active or passive. This distinction depends on whether the polymer influences charge or mass transport in the electrode. Though it is desirable to understand how to tailor the macromolecular design of a polymer to play a passive or active role, design rules are still lacking, as is a framework to assess the divergence in such behaviors. We reveal the molecular-level underpinnings that distinguish an active polyelectrolyte binder designed for lithium-sulfur batteries from a passive alternative. The binder, a cationic polyelectrolyte, is shown to both facilitate lithium-ion transport through its reconfigurable network ofmore » mobile anions and restrict polysulfide diffusion from mesoporous carbon hosts by anion metathesis, which we show is selective for higher oligomers. These attributes then allow cells to be operated for > 100 cycles with excellent rate capability using cathodes with areal sulfur loadings up to 8.1 mg cm -2 .« less

Pt-Au/MOx-CeO₂ (M = Mn, Fe, Ti) Catalysts for the Co-Oxidation of CO and H₂ at Room Temperature.

PubMed

Hong, Xiaowei; Sun, Ye; Zhu, Tianle; Liu, Zhiming

2017-02-27

A series of nanostructured Pt-Au/MO x -CeO₂ (M = Mn, Fe, Ti) catalysts were prepared and their catalytic performance for the co-oxidation of carbon monoxide (CO) and hydrogen (H₂) were evaluated at room temperature. The results showed that MO x promoted the CO oxidation of Pt-Au/CeO₂, but only the TiO₂ could enhance co-oxidation of CO and H₂ over Pt-Au/CeO₂. Related characterizations were conducted to clarify the promoting effect of MO x . Temperature-programmed reduction of hydrogen (H₂-TPR) and X-ray photoelectron spectroscopy (XPS) results suggested that MO x could improve the charge transfer from Au sites to CeO₂, resulting in a high concentration of Ce 3+ and cationic Au species which benefits for the CO oxidation. In-situ diffuse reflectance infrared Fourier transform spectroscopy (In-situ DRIFTS) results indicated that TiO₂ could facilitate the oxidation of H₂ over the Pt-Au/TiO₂-CeO₂ catalyst.

Extrinsic Cation Selectivity of 2D Membranes

PubMed Central

2017-01-01

From a systematic study of the concentration driven diffusion of positive and negative ions across porous 2D membranes of graphene and hexagonal boron nitride (h-BN), we prove their cation selectivity. Using the current–voltage characteristics of graphene and h-BN monolayers separating reservoirs of different salt concentrations, we calculate the reversal potential as a measure of selectivity. We tune the Debye screening length by exchanging the salt concentrations and demonstrate that negative surface charge gives rise to cation selectivity. Surprisingly, h-BN and graphene membranes show similar characteristics, strongly suggesting a common origin of selectivity in aqueous solvents. For the first time, we demonstrate that the cation flux can be increased by using ozone to create additional pores in graphene while maintaining excellent selectivity. We discuss opportunities to exploit our scalable method to use 2D membranes for applications including osmotic power conversion. PMID:28157333

Supramolecular architecture based on [Fe(CN)6]3- metallotectons and melaminium synthons

NASA Astrophysics Data System (ADS)

Krichen, Firas; Walha, Siwar; Lhoste, Jérôme; Bulou, Alain; Kabadou, Ahlem; Goutenoire, François

2017-10-01

Assembly involving [Fe(CN)6]3- metallotectons as building units and melaminium organic cation has been envisioned in order to elaborate a hybrid supramolecular based on ionic H-bonds with formula {(H-mel)4[Fe(CN)6]Cl} (H-mel+: melaminium cation). The compound has been prepared by diffusion method and characterized by single-crystal X-ray diffraction, EDX analysis, and Raman-IR spectroscopies with assignment from ab initio calculations. The melaminium exhibit self cationic coupling with cyclic hydrogen bonds to give a one dimensional {[H-mel]+}∝ synthon. Therefore, these cationic ribbons are inter-linked via hydrogen bonds by the anionic tectons [Fe(CN)6]3- and chlorine anion resulting on a 3D network. Molecular hirshfeld surfaces revealed that the crystal structure has been supported mainly by Nsbnd H⋯N and Nsbnd H⋯Cl intermolecular Hydrogen bonds and by favoured C⋯C and C⋯N weak interactions.

Huntingtin regulates Ca(2+) chemotaxis and K(+)-facilitated cAMP chemotaxis, in conjunction with the monovalent cation/H(+) exchanger Nhe1, in a model developmental system: insights into its possible role in Huntington׳s disease.

PubMed

Wessels, Deborah; Lusche, Daniel F; Scherer, Amanda; Kuhl, Spencer; Myre, Michael A; Soll, David R

2014-10-01

Huntington׳s disease is a neurodegenerative disorder, attributable to an expanded trinucleotide repeat in the coding region of the human HTT gene, which encodes the protein huntingtin. These mutations lead to huntingtin fragment inclusions in the striatum of the brain. However, the exact function of normal huntingtin and the defect causing the disease remain obscure. Because there are indications that huntingtin plays a role in Ca(2+) homeostasis, we studied the deletion mutant of the HTT ortholog in the model developmental system Dictyostelium discoideum, in which Ca(2+) plays a role in receptor-regulated behavior related to the aggregation process that leads to multicellular morphogenesis. The D. discoideum htt(-)-mutant failed to undergo both K(+)-facilitated chemotaxis in spatial gradients of the major chemoattractant cAMP, and chemotaxis up a spatial gradient of Ca(2+), but behaved normally in Ca(2+)-facilitated cAMP chemotaxis and Ca(2+)-dependent flow-directed motility. This was the same phenotypic profile of the null mutant of Nhel, a monovalent cation/H(+)exchanger. The htt(-)-mutant also failed to orient correctly during natural aggregation, as was the case for the Nhel mutant. Moreover, in a K(+)-based buffer the normal localization of actin was similarly defective in both htt(-) and nhe1(-) cells in a K(+)-based buffer, and the normal localization of Nhe1 was disrupted in the htt(-) mutant. These observations demonstrate that Htt and Nhel play roles in the same specific cation-facilitated behaviors and that Nhel localization is directly or indirectly regulated by Htt. Similar cation-dependent behaviors and a similar relationship between Htt and Nhe1 have not been reported for mammalian neurons and deserves investigation, especially as it may relate to Huntington׳s disease. Copyright © 2014 Elsevier Inc. All rights reserved.

Ion Pairing and Diffusion in Magnesium Electrolytes Based on Magnesium Borohydride.

PubMed

Samuel, Devon; Steinhauser, Carl; Smith, Jeffrey G; Kaufman, Aaron; Radin, Maxwell D; Naruse, Junichi; Hiramatsu, Hidehiko; Siegel, Donald J

2017-12-20

One obstacle to realizing a practical, rechargeable magnesium-ion battery is the development of efficient Mg electrolytes. Electrolytes based on simple Mg(BH 4 ) 2 salts suffer from poor salt solubility and/or low conductivity, presumably due to strong ion pairing. Understanding the molecular-scale processes occurring in these electrolytes would aid in overcoming these performance limitations. Toward this goal, the present study examines the solvation, agglomeration, and transport properties of a family of Mg electrolytes based on the Mg(BH 4 ) 2 salt using classical molecular dynamics. These properties were examined across five different solvents (tetrahydrofuran and the glymes G1-G4) and at four salt concentrations ranging from the dilute limit up to 0.4 M. Significant and irreversible salt agglomeration was observed in all solvents at all nondilute Mg(BH 4 ) 2 concentrations. The degree of clustering observed in these divalent Mg systems is much larger than that reported for electrolytes containing monovalent cations, such as Li. The salt agglomeration rate and diffusivity of Mg 2+ were both observed to correlate with solvent self-diffusivity: electrolytes using longer- (shorter-) chain solvents had the lowest (highest) Mg 2+ diffusivity and agglomeration rates. Incorporation of Mg 2+ into Mg 2+ -BH 4 - clusters significantly reduces the diffusivity of Mg 2+ by restricting displacements to localized motion within largely immobile agglomerates. Consequently, diffusion is increasingly impeded with increasing Mg(BH 4 ) 2 concentration. These data are consistent with the solubility limitations observed experimentally for Mg(BH 4 ) 2 -based electrolytes and highlight the need for strategies that minimize salt agglomeration in electrolytes containing divalent cations.

Myoglobin translational diffusion in rat myocardium and its implication on intracellular oxygen transport.

PubMed

Lin, Ping-Chang; Kreutzer, Ulrike; Jue, Thomas

2007-01-15

Current theory of respiratory control invokes a role of myoglobin (Mb)-facilitated O2 diffusion in regulating the intracellular O2 flux, provided Mb diffusion can compete effectively with free O2 diffusion. Pulsed-field gradient NMR methods have now followed gradient-dependent changes in the distinct 1H NMR gamma CH3 Val E11 signal of MbO2 in perfused rat myocardium to obtain the endogenous Mb translational diffusion coefficient (D(Mb)) of 4.24 x 10(-7) cm2 s(-1) at 22 degrees C. The D(Mb) matches precisely the value predicted by in vivo NMR rotational diffusion measurements of Mb and shows no orientation preference. Given values in the literature for the Krogh's free O2 diffusion coefficient (K0), myocardial Mb concentration and a partial pressure of O2 that half saturates Mb (P50), the analysis yields an equipoise diffusion P(O2) of 1.77 mmHg, where Mb and free O2 contribute equally to the O2 flux. In the myocardium, Mb-facilitated O2 diffusion contributes increasingly more than free O2 diffusion when the P(O2) falls below 1.77 mmHg. In skeletal muscle, the P(O2) must fall below 5.72 mmHg. Altering the Mb P50 induces modest change. Mb-facilitated diffusion has a higher poise in skeletal muscle than in myocardium. Because the basal P(O2) hovers around 10 mmHg, Mb does not have a predominant role in facilitating O2 transport in myocardium but contributes significantly only when cellular oxygen falls below the equipoise diffusion P(O2).

One-pot template-free synthesis of monodisperse hollow hydrogel microspheres and their resulting properties.

PubMed

Lim, Hyung-Seok; Kwon, Eunji; Lee, Moonjoo; Moo Lee, Young; Suh, Kyung-Do

2013-08-01

Monodisperse poly(methacrylic acid/ethyleneglycoldimethacrylate) (MAA/EGDMA) hollow microcapsules, which exhibit pH-responsive behavior, are prepared by diffusion of cationic surfactants and hydrophobic interaction. During the association of the negatively charged hydrogel microspheres and an oppositely charged surfactant (cetyltrimethylammonium bromide, CTA(+)B), the hydrophobic polymer-surfactant complexes that form are separated from the internal water; consequently, a hollow structure can be formed. Confocal laser scanning microscopy, UV spectro-scopy and zeta potential are employed to study the formation of the hollow structure during the diffusion of the cationic surfactant. The controlled release behavior of methylene blue as a model drug from the as-prepared poly(MAA/EGDMA) microcapsules with a hollow structure is investigated under different pH conditions. The hollow structure can be retained, even during repetitive pH changes. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

The ultraviolet and visible spectrum of the polycyclic aromatic hydrocarbon C10H8(+) - Possible contributions to the diffuse interstellar bands and to the ultraviolet-visible extinction

NASA Technical Reports Server (NTRS)

Salama, F.; Allamandola, L. J.

1992-01-01

The properties of the cation of the PAH naphthalene (C10H8(+)) isolated in inert gas matrices under conditions relevant to astrophysical environments are described. The band at 6741 A is the strongest and falls close to the weak 6742 A diffuse interstellar bands (DIBs). Five other weaker bands also fall remarkably close to the positions of known DIBs. A very intense and broad continuum extended from the UV to the visible, which seems to be associated with the ion, is reported. The molar absorption coefficient at the peak of the continuum is 2.0 x 10 exp 6 cu dm/mol cm. If a continuum is a general property of PAH cations, this characteristic will have a strong impact on the understanding of how PAHs convert interstellar UV and visible radiation into IR radiation.

Bipolar membranes with fluid distribution passages

NASA Technical Reports Server (NTRS)

Hitchens, G. Duncan (Inventor); Archer, Shivaun (Inventor); Tennakoon, Charles L. (Inventor); Gonzalez-Martin, Anuncia (Inventor); Cisar, Alan J. (Inventor)

1999-01-01

The present invention provides a bipolar membrane and methods for making and using the membrane. The bipolar membrane comprises a cation-selective region, an anion-selective region, an interfacial region between the anion-selective region and the cation-selective region, and means for delivering fluid directly into the interfacial region. The means for delivering fluid includes passages that may comprise a fluid-permeable material, a wicking material, an open passage disposed within the membrane or some combination thereof. The passages may be provided in many shapes, sizes and configurations, but preferably deliver fluid directly to the interfacial region so that the rate of electrodialysis is no longer limited by the diffusion of fluid through the cation- or anion-selective regions to the interfacial region.

The SLC3 and SLC7 families of amino acid transporters.

PubMed

Fotiadis, Dimitrios; Kanai, Yoshikatsu; Palacín, Manuel

2013-01-01

Amino acids are necessary for all living cells and organisms. Specialized transporters mediate the transfer of amino acids across plasma membranes. Malfunction of these proteins can affect whole-body homoeostasis giving raise to diverse human diseases. Here, we review the main features of the SLC3 and SLC7 families of amino acid transporters. The SLC7 family is divided into two subfamilies, the cationic amino acid transporters (CATs), and the L-type amino acid transporters (LATs). The latter are the light or catalytic subunits of the heteromeric amino acid transporters (HATs), which are associated by a disulfide bridge with the heavy subunits 4F2hc or rBAT. These two subunits are glycoproteins and form the SLC3 family. Most CAT subfamily members were functionally characterized and shown to function as facilitated diffusers mediating the entry and efflux of cationic amino acids. In certain cells, CATs play an important role in the delivery of L-arginine for the synthesis of nitric oxide. HATs are mostly exchangers with a broad spectrum of substrates and are crucial in renal and intestinal re-absorption and cell redox balance. Furthermore, the role of the HAT 4F2hc/LAT1 in tumor growth and the application of LAT1 inhibitors and PET tracers for reduction of tumor progression and imaging of tumors are discussed. Finally, we describe the link between specific mutations in HATs and the primary inherited aminoacidurias, cystinuria and lysinuric protein intolerance. Copyright © 2012 Elsevier Ltd. All rights reserved.

Azole drugs are imported by facilitated diffusion in Candida albicans and other pathogenic fungi.

PubMed

Mansfield, Bryce E; Oltean, Hanna N; Oliver, Brian G; Hoot, Samantha J; Leyde, Sarah E; Hedstrom, Lizbeth; White, Theodore C

2010-09-30

Despite the wealth of knowledge regarding the mechanisms of action and the mechanisms of resistance to azole antifungals, very little is known about how the azoles are imported into pathogenic fungal cells. Here the in-vitro accumulation and import of Fluconazole (FLC) was examined in the pathogenic fungus, Candida albicans. In energized cells, FLC accumulation correlates inversely with expression of ATP-dependent efflux pumps. In de-energized cells, all strains accumulate FLC, suggesting that FLC import is not ATP-dependent. The kinetics of import in de-energized cells displays saturation kinetics with a K(m) of 0.64 μM and V(max) of 0.0056 pmol/min/10⁸ cells, demonstrating that FLC import proceeds via facilitated diffusion through a transporter rather than passive diffusion. Other azoles inhibit FLC import on a mole/mole basis, suggesting that all azoles utilize the same facilitated diffusion mechanism. An analysis of related compounds indicates that competition for azole import depends on an aromatic ring and an imidazole or triazole ring together in one molecule. Import of FLC by facilitated diffusion is observed in other fungi, including Cryptococcus neoformans, Saccharomyces cerevisiae, and Candida krusei, indicating that the mechanism of transport is conserved among fungal species. FLC import was shown to vary among Candida albicans resistant clinical isolates, suggesting that altered facilitated diffusion may be a previously uncharacterized mechanism of resistance to azole drugs.

Effect of the pore water composition on the diffusive anion transport in argillaceous, low permeability sedimentary rocks

NASA Astrophysics Data System (ADS)

Wigger, Cornelia; Van Loon, Luc R.

2018-06-01

The effect of the pore water composition on the diffusive anion transport was studied for two different argillaceous, low permeability sedimentary rocks, Opalinus Clay (OPA) and Helvetic Marl (HM). The samples were saturated with different solutions with varying molar concentration and different main cations in the solution: NaCl based pore solutions and CaCl2 based pore solutions. The total porosity was measured by through-diffusion experiments with the neutral tracer HTO. Experiments performed in NaCl solutions resulted in a porosity of 0.12 for OPA and 0.03 for HM, and are consistent with results of the experiments in CaCl2 solutions. The total porosity was independent of the molar concentration, in contrast to the measured anion porosity, which increased with increasing molar concentration. It could further be observed that the pore solution based on the bivalent cation calcium shielded the negative surface charge stronger than the monovalent cation sodium, resulting in a larger measureable anion-accessible porosity in the case of CaCl2 solutions. The data was modelled based on an adapted Donnan approach of Birgersson and Karnland (2009). The model had to be adjusted with a permanent free, uncharged porosity, as well as with structural information on the permanent anion exclusion because of so-called bottleneck pores. Both parameters can only be evaluated from experiments. Nevertheless, taking these two adaptions into account, the effect of varying pore water compositions on the anion-accessible porosity of the investigated argillaceous rocks could be satisfactorily described.

Driving mechanisms of ionic polymer actuators having electric double layer capacitor structures.

PubMed

Imaizumi, Satoru; Kato, Yuichi; Kokubo, Hisashi; Watanabe, Masayoshi

2012-04-26

Two solid polymer electrolytes, composed of a polyether-segmented polyurethaneurea (PEUU) and either a lithium salt (lithium bis(trifluoromethanesulfonyl)amide: Li[NTf2]) or a nonvolatile ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide: [C2mim][NTf2]), were prepared in order to utilize them as ionic polymer actuators. These salts were preferentially dissolved in the polyether phases. The ionic transport mechanism of the polyethers was discussed in terms of the diffusion coefficients and ionic transference numbers of the incorporated ions, which were estimated by means of pulsed-field gradient spin-echo (PGSE) NMR. There was a distinct difference in the ionic transport properties of each polymer electrolyte owing to the difference in the magnitude of interactions between the cations and the polyether. The anionic diffusion coefficient was much faster than that of the cation in the polyether/Li[NTf2] electrolyte, whereas the cation diffused faster than the anion in the polyether/[C2mim][NTf2] electrolyte. Ionic polymer actuators, which have a solid-state electric-double-layer-capacitor (EDLC) structure, were prepared using these polymer electrolyte membranes and ubiquitous carbon materials such as activated carbon and acetylene black. On the basis of the difference in the motional direction of each actuator against applied voltages, a simple model of the actuation mechanisms was proposed by taking the difference in ionic transport properties into consideration. This model discriminated the behavior of the actuators in terms of the products of transference numbers and ionic volumes. The experimentally observed behavior of the actuators was successfully explained by this model.

First principles molecular dynamics of molten NaI: Structure, self-diffusion, polarization effects, and charge transfer

NASA Astrophysics Data System (ADS)

Galamba, N.; Costa Cabral, B. J.

2007-09-01

The structure and self-diffusion of NaI and NaCl at temperatures close to their melting points are studied by first principles Hellmann-Feynman molecular dynamics (HFMD). The results are compared with classical MD using rigid-ion (RI) and shell-model (ShM) interionic potentials. HFMD for NaCl was reported before at a higher temperature [N. Galamba and B. J. Costa Cabral, J. Chem. Phys. 126, 124502 (2007)]. The main differences between the structures predicted by HFMD and RI MD for NaI concern the cation-cation and the anion-cation pair correlation functions. A ShM which allows only for the polarization of I- reproduces the main features of the HFMD structure of NaI. The inclusion of polarization effects for both ionic species leads to a more structured ionic liquid, although a good agreement with HFMD is also observed. HFMD Green-Kubo self-diffusion coefficients are larger than those obtained from RI and ShM simulations. A qualitative study of charge transfer in molten NaI and NaCl was also carried out with the Hirshfeld charge partitioning method. Charge transfer in molten NaI is comparable to that in NaCl, and results for NaCl at two temperatures support the view that the magnitude of charge transfer is weakly state dependent for ionic systems. Finally, Hirshfeld charge distributions indicate that differences between RI and HFMD results are mainly related to polarization effects, while the influence of charge transfer fluctuations is minimal for these systems.

Effect of the pore water composition on the diffusive anion transport in argillaceous, low permeability sedimentary rocks.

PubMed

Wigger, Cornelia; Van Loon, Luc R

2018-06-01

The effect of the pore water composition on the diffusive anion transport was studied for two different argillaceous, low permeability sedimentary rocks, Opalinus Clay (OPA) and Helvetic Marl (HM). The samples were saturated with different solutions with varying molar concentration and different main cations in the solution: NaCl based pore solutions and CaCl 2 based pore solutions. The total porosity was measured by through-diffusion experiments with the neutral tracer HTO. Experiments performed in NaCl solutions resulted in a porosity of 0.12 for OPA and 0.03 for HM, and are consistent with results of the experiments in CaCl 2 solutions. The total porosity was independent of the molar concentration, in contrast to the measured anion porosity, which increased with increasing molar concentration. It could further be observed that the pore solution based on the bivalent cation calcium shielded the negative surface charge stronger than the monovalent cation sodium, resulting in a larger measureable anion-accessible porosity in the case of CaCl 2 solutions. The data was modelled based on an adapted Donnan approach of Birgersson and Karnland (2009). The model had to be adjusted with a permanent free, uncharged porosity, as well as with structural information on the permanent anion exclusion because of so-called bottleneck pores. Both parameters can only be evaluated from experiments. Nevertheless, taking these two adaptions into account, the effect of varying pore water compositions on the anion-accessible porosity of the investigated argillaceous rocks could be satisfactorily described. Copyright © 2018 Elsevier B.V. All rights reserved.

On two alternative mechanisms of ethane activation over ZSM-5 zeolite modified by Zn2+ and Ga1+ cations.

PubMed

Kazansky, V B; Subbotina, I R; Rane, N; van Santen, R A; Hensen, E J M

2005-08-21

The activation of ethane over zinc- and gallium-modified HZSM-5 dehydrogenation catalysts was studied by diffuse reflectance infrared spectroscopy. Hydrocarbon activation on HZSM-5 modified by bivalent Zn and univalent Ga cations proceeds via two distinctly different mechanisms. The stronger molecular adsorption of ethane by the acid-base pairs formed by distantly separated cationic Zn2+ and basic oxygen sites results already at room temperature in strong polarizability of adsorbed ethane and subsequent heterolytic dissociative adsorption at moderate temperatures. In contrast, molecular adsorption of ethane on Ga+ cations is weak. At high temperatures dissociative hydrocarbon adsorption takes place, resulting in the formation of ethyl and hydride fragments coordinating to the cationic gallium species. Whereas in the zinc case a Brønsted acid proton is formed upon ethane dissociation, decomposition of the ethyl fragment on gallium results in gallium dihydride species and does not lead to Brønsted acid protons. This difference in alkane activation has direct consequences for hydrocarbon conversions involving dehydrogenation.

Diffusion of neutral and ionic species in charged membranes: boric acid, arsenite, and water.

PubMed

Goli, Esmaiel; Hiemstra, Tjisse; Van Riemsdijk, Willem H; Rahnemaie, Rasoul; Malakouti, Mohammad Jafar

2010-10-15

Dynamic ion speciation using DMT (Donnan membrane technique) requires insight into the physicochemical characteristics of diffusion in charged membranes (tortuosity, local diffusion coefficients) as well as ion accumulation. The latter can be precluded by studying the diffusion of neutral species, such as boric acid, B(OH)₃⁰(aq), arsenite, As(OH)₃⁰(aq), or water. In this study, the diffusion rate of B(OH)₃⁰ has been evaluated as a function of the concentration, pH, and ionic strength. The rate is linearly dependent on the concentration of solely the neutral species, without a significant contribution of negatively charged species such as B(OH)₄⁻, present at high pH. A striking finding is the very strong effect (factor of ~10) of the type of cation (K(+), Na(+), Ca(2+), Mg(2+), Al(3+), and H(+)) on the diffusion coefficient of B(OH)₃⁰ and also As(OH)₃⁰. The decrease of the diffusion coefficient can be rationalized as an enhancement of the mean viscosity of the confined solution in the membrane. The diffusion coefficients can be described by a semiempirical relationship, linking the mean viscosity of the confined solute of the membrane to the viscosity of the free solution. In proton-saturated membranes, as used in fuel cells, viscosity is relatively more enhanced; i.e., a stronger water network is formed. Extraordinarily, our B(OH)₃-calibrated model (in HNO₃) correctly predicts the reported diffusion coefficient of water (D(H₂O)), measured with ¹H NMR and quasi-elastic neutron scattering in H(+)-Nafion membranes. Upon drying these membranes, the local hydronium, H(H₂O)(n)(+), concentration and corresponding viscosity increase, resulting in a severe reduction of the diffusion coefficient (D(H₂O) ≈ 5-50 times), in agreement with the model. The present study has a second goal, i.e., development of the methodology for measuring the free concentration of neutral species in solution. Our data suggest that the free concentration can be measured with DMT in natural systems if one accounts for the variation in the cation composition of the membrane and corresponding viscosity/diffusion coefficient.

NMR Study of Ion Dynamics and Charge Storage in Ionic Liquid Supercapacitors

PubMed Central

2015-01-01

Ionic liquids are emerging as promising new electrolytes for supercapacitors. While their higher operating voltages allow the storage of more energy than organic electrolytes, they cannot currently compete in terms of power performance. More fundamental studies of the mechanism and dynamics of charge storage are required to facilitate the development and application of these materials. Here we demonstrate the application of nuclear magnetic resonance spectroscopy to study the structure and dynamics of ionic liquids confined in porous carbon electrodes. The measurements reveal that ionic liquids spontaneously wet the carbon micropores in the absence of any applied potential and that on application of a potential supercapacitor charging takes place by adsorption of counterions and desorption of co-ions from the pores. We find that adsorption and desorption of anions surprisingly plays a more dominant role than that of the cations. Having elucidated the charging mechanism, we go on to study the factors that affect the rate of ionic diffusion in the carbon micropores in an effort to understand supercapacitor charging dynamics. We show that the line shape of the resonance arising from adsorbed ions is a sensitive probe of their effective diffusion rate, which is found to depend on the ionic liquid studied, as well as the presence of any solvent additives. Taken as whole, our NMR measurements allow us to rationalize the power performances of different electrolytes in supercapacitors. PMID:25973552

Electrochemical evidences and consequences of significant differences in ions diffusion rate in polyacrylate-based ion-selective membranes.

PubMed

Woźnica, Emilia; Mieczkowski, Józef; Michalska, Agata

2011-11-21

The origin and effect of surface accumulation of primary ions within the ion-selective poly(n-butyl acrylate)-based membrane, obtained by thermal polymerization, is discussed. Using a new method, based on the relation between the shape of a potentiometric plot and preconditioning time, the diffusion of copper ions in the membrane was found to be slow (the diffusion coefficient estimated to be close to 10(-11) cm(2) s(-1)), especially when compared to ion-exchanger counter ions--sodium cations diffusion (a diffusion coefficient above 10(-9) cm(2) s(-1)). The higher mobility of sodium ions than those of the copper-ionophore complex results in exposed ion-exchanger role leading to undesirably exposed sensitivity to sodium or potassium ions.

Contrast-enhanced CT with a High-Affinity Cationic Contrast Agent for Imaging ex Vivo Bovine, Intact ex Vivo Rabbit, and in Vivo Rabbit Cartilage

PubMed Central

Stewart, Rachel C.; Bansal, Prashant N.; Entezari, Vahid; Lusic, Hrvoje; Nazarian, Rosalynn M.; Snyder, Brian D.

2013-01-01

Purpose: To quantify the affinity of a cationic computed tomography (CT) contrast agent (CA4+) and that of an anionic contrast agent (ioxaglate) to glycosaminoglycans (GAGs) in ex vivo cartilage tissue explants and to characterize the in vivo diffusion kinetics of CA4+ and ioxaglate in a rabbit model. Materials and Methods: All in vivo procedures were approved by the institutional animal care and use committee. The affinities of ioxaglate and CA4+ to GAGs in cartilage (six bovine osteochondral plugs) were quantified by means of a modified binding assay using micro-CT after plug equilibration in serial dilutions of each agent. The contrast agents were administered intraarticularly to the knee joints of five New Zealand white rabbits to determine the in vivo diffusion kinetics and cartilage tissue imaging capabilities. Kinetics of diffusion into the femoral groove cartilage and relative contrast agent uptake into bovine plugs were characterized by means of nonlinear mixed-effects models. Diffusion time constants (τ) were compared by using a Student t test. Results: The uptake of CA4+ in cartilage was consistently over 100% of the reservoir concentration, whereas it was only 59% for ioxaglate. In vivo, the contrast material–enhanced cartilage reached a steady CT attenuation for both CA4+ and ioxaglate, with τ values of 13.8 and 6.5 minutes, respectively (P = .04). The cartilage was easily distinguishable from the surrounding tissues for CA4+ (12 mg of iodine per milliliter); comparatively, the anionic contrast agent provided less favorable imaging results, even when a higher concentration was used (80 mg of iodine per milliliter). Conclusion: The affinity of the cationic contrast agent CA4+ to GAGs enables high-quality imaging and segmentation of ex vivo bovine and rabbit cartilage, as well as in vivo rabbit cartilage. © RSNA, 2012 Supplemental material: http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.12112246/-/DC1 PMID:23192774

Sorption of Sr, Co and Zn on illite: Batch experiments and modelling including Co in-diffusion measurements on compacted samples

NASA Astrophysics Data System (ADS)

Montoya, V.; Baeyens, B.; Glaus, M. A.; Kupcik, T.; Marques Fernandes, M.; Van Laer, L.; Bruggeman, C.; Maes, N.; Schäfer, T.

2018-02-01

Experimental investigations on the uptake of divalent cations (Sr, Co and Zn) onto illite (Illite du Puy, Le-Puy-en-Velay, France) were carried out by three different international research groups (Institute for Nuclear Waste Disposal, KIT (Germany), Group Waste & Disposal, SCK-CEN, (Belgium) and Laboratory for Waste Management, PSI (Switzerland)) in the framework of the European FP7 CatClay project. The dependence of solid-liquid distribution ratios (Rd values) on pH at trace metal conditions (sorption edges) and on the metal ion concentration (sorption isotherms) was determined in dilute suspensions of homo-ionic Na-illite (Na-IdP) under controlled N2 atmosphere. The experimental results were modelled using the 2 Site Protolysis Non Electrostatic Surface Complexation and Cation Exchange (2SPNE SC/CE) sorption model. The sorption of Sr depends strongly on ionic strength, while a rather weak pH dependence is observed in a pH range between 3 and 11. The data were modelled with cation exchange reactions, taking into account competition with H, K, Ca, Mg and Al, and surface complexation on weak amphotheric edge sites at higher pH values. The sorption of Co on Na-IdP, however, is strongly pH dependent. Cation exchange on the planar sites and surface complexation on strong and weak amphoteric edge sites were used to describe the Co sorption data. Rd values for Co derived from in-diffusion measurements on compacted Na-IdP samples (bulk-dry density of 1700 kg m-3) between pH 5.0 and 9.0 are in good agreement with the batch sorption data. The equivalence of both approaches to measure sorption was thus confirmed for the present test system. In addition, the results highlight the importance of both major and minor surface species for the diffusive transport behaviour of strongly sorbing metal cations. While surface complexes at the edge sites determine largely the Rd value, the diffusive flux may be governed by those species bound to the planar sites, even at low fractional occupancies. The pH dependent sorption determined for trace Zn concentrations showed large Rd values across the entire pH range with almost no dependence on the background electrolyte concentration. Additional sorption experiments carried out at substantial fractional Zn loadings demonstrated that the selectivity for the exchange of Na+ for Zn2+ at the planar sites could not explain the large Rd values measured at low pH and trace Zn concentrations. This suggests that another mechanism is ruling Zn uptake under these conditions.

Fluctuation-enhanced electric conductivity in electrolyte solutions.

PubMed

Péraud, Jean-Philippe; Nonaka, Andrew J; Bell, John B; Donev, Aleksandar; Garcia, Alejandro L

2017-10-10

We analyze the effects of an externally applied electric field on thermal fluctuations for a binary electrolyte fluid. We show that the fluctuating Poisson-Nernst-Planck (PNP) equations for charged multispecies diffusion coupled with the fluctuating fluid momentum equation result in enhanced charge transport via a mechanism distinct from the well-known enhancement of mass transport that accompanies giant fluctuations. Although the mass and charge transport occurs by advection by thermal velocity fluctuations, it can macroscopically be represented as electrodiffusion with renormalized electric conductivity and a nonzero cation-anion diffusion coefficient. Specifically, we predict a nonzero cation-anion Maxwell-Stefan coefficient proportional to the square root of the salt concentration, a prediction that agrees quantitatively with experimental measurements. The renormalized or effective macroscopic equations are different from the starting PNP equations, which contain no cross-diffusion terms, even for rather dilute binary electrolytes. At the same time, for infinitely dilute solutions the renormalized electric conductivity and renormalized diffusion coefficients are consistent and the classical PNP equations with renormalized coefficients are recovered, demonstrating the self-consistency of the fluctuating hydrodynamics equations. Our calculations show that the fluctuating hydrodynamics approach recovers the electrophoretic and relaxation corrections obtained by Debye-Huckel-Onsager theory, while elucidating the physical origins of these corrections and generalizing straightforwardly to more complex multispecies electrolytes. Finally, we show that strong applied electric fields result in anisotropically enhanced "giant" velocity fluctuations and reduced fluctuations of salt concentration.

Prediction of Intrinsic Cesium Desorption from Na-Smectite in Mixed Cation Solutions.

PubMed

Fukushi, Keisuke; Fukiage, Tomo

2015-09-01

Quantitative understanding of the stability of sorbed radionuclides in smectite is necessary to assess the performance of engineering barriers used for nuclear waste disposal. Our previous study demonstrated that the spatial organization of the smectite platelets triggered by the divalent cations led to the apparent fixation of intrinsic Cs in smectite, because some Cs is retained inside the formed tactoids. Natural water is usually a mixture of Na(+) and divalent cations (Ca(2+) and Mg(2+)). This study therefore investigated the desorption behavior of intrinsic Cs in Na-smecite in mixed Na(+)-divalent cation solutions under widely various cation concentrations using batch experiments, grain size measurements, and cation exchange modeling (CEM). Results show that increased Na(+) concentrations facilitate Cs desorption because Na(+) serves as the dispersion agent. A linear relation was obtained between the logarithm of the Na(+) fraction and the accessible Cs fraction in smectite. That relation enables the prediction of accessible Cs fraction as a function of solution cationic compositions. The corrected CEM considering the effects of the spatial organization suggests that the stability of intrinsic Cs in the smectite is governed by the Na(+) concentration, and suggests that it is almost independent of the concentrations of divalent cations in natural water.

Dissociation of protonated N-(3-phenyl-2H-chromen-2-ylidene)-benzenesulfonamide in the gas phase: cyclization via sulfonyl cation transfer.

PubMed

Wang, Shanshan; Dong, Cheng; Yu, Lian; Guo, Cheng; Jiang, Kezhi

2016-01-15

In the tandem mass spectrometry of protonated N-(3-phenyl-2H-chromen-2-ylidene)benzenesulfonamides, the precursor ions have been observed to undergo gas-phase dissociation via two competing channels: (a) the predominant channel involves migration of the sulfonyl cation to the phenyl C atom and the subsequent loss of benzenesulfinic acid along with cyclization reaction, and (b) the minor one involves dissociation of the precursor ion to give an ion/neutral complex of [sulfonyl cation/imine], followed by decomposition to afford sulfonyl cation or the INC-mediated electron transfer to give an imine radical cation. The proposed reaction channels have been supported by theoretical calculations and D-labeling experiments. The gas-phase cyclization reaction originating from the N- to C-sulfonyl cation transfer has been first reported to the best of our knowledge. For the substituted sulfonamides, the presence of electron-donating groups (R(2) -) at the C-ring effectively facilitates the reaction channel of cyclization reaction, whereas that of electron-withdrawing groups inhibits this pathway. Copyright © 2015 John Wiley & Sons, Ltd.

The reduction mechanism of chromite in the presence of a silica flux

NASA Astrophysics Data System (ADS)

Weber, P.; Eric, R. H.

1993-12-01

The reduction behavior of a natural chromite from the Bushveld Complex of South Africa was studied at 1300 °C to 1500 °C. Reduction was by graphite in the presence of silica. Thermo-gravimetric analysis, X-ray diffraction (XRD) analysis, energy-dispersive X-ray analysis (EDAX), and metallographic analysis were the experimental techniques used. Silica affected the reduction at and above 1400 °C. A two-stage reduction mechanism was established. The first stage, up to a reduction level of about 40 pct, is primarily confined to iron metallization, and zoning is observed in partially reduced chromites. In this stage, silica does not interfere with the reduction, which proceeds by an outward diffusion of Fe2+ ions and an inward diffusion of Mg2+ and Cr2+ ions. The second stage is primarily confined to chromium metallization, and formation of a silicate slag alters the reduction mechanism. The slag phase agglomerates and even embeds partially reduced chromite particles. An ion-exchange reaction between the re-ducible cations (Cr3+ and Fe2+) in the spinel and the dissolved cations (Al3+ and Mg2+) in the slag allows further reduction. Once the reducible cations are dissolved in the slag phase, they are reduced to the metallic state at sites where there is contact with the reductant.

Impact of ionic liquids in aqueous solution on bacterial plasma membranes studied with molecular dynamics simulations.

PubMed

Lim, Geraldine S; Zidar, Jernej; Cheong, Daniel W; Jaenicke, Stephan; Klähn, Marco

2014-09-04

The impact of five different imidazolium-based ionic liquids (ILs) diluted in water on the properties of a bacterial plasma membrane is investigated using molecular dynamics (MD) simulations. Cations considered are 1-octyl-3-methylimidazolium (OMIM), 1-octyloxymethyl-3-methylimidazolium (OXMIM), and 1-tetradecyl-3-methylimidazolium (TDMIM), as well as the anions chloride and lactate. The atomistic model of the membrane bilayer is designed to reproduce the lipid composition of the plasma membrane of Gram-negative Escherichia coli. Spontaneous insertion of cations into the membrane is observed in all ILs. Substantially more insertions of OMIM than of OXMIM occur and the presence of chloride reduces cation insertions compared to lactate. In contrast, anions do not adsorb onto the membrane surface nor diffuse into the bilayer. Once inserted, cations are oriented in parallel to membrane lipids with cation alkyl tails embedded into the hydrophobic membrane core, while the imidazolium-ring remains mostly exposed to the solvent. Such inserted cations are strongly associated with one to two phospholipids in the membrane. The overall order of lipids decreased after OMIM and OXMIM insertions, while on the contrary the order of lipids in the vicinity of TDMIM increased. The short alkyl tails of OMIM and OXMIM generate voids in the bilayer that are filled by curling lipids. This cation induced lipid disorder also reduces the average membrane thickness. This effect is not observed after TDMIM insertions due to the similar length of cation alkyl chain and the fatty acids of the lipids. This lipid-mimicking behavior of inserted TDMIM indicates a high membrane affinity of this cation that could lead to an enhanced accumulation of cations in the membrane over time. Overall, the simulations reveal how cations are inserted into the bacterial membrane and how such insertions change its properties. Moreover, the different roles of cations and anions are highlighted and the fundamental importance of cation alkyl chain length and its functionalization is demonstrated.

Golgi Localized Barley MTP8 Proteins Facilitate Mn Transport

PubMed Central

Pedas, Pai; Schiller Stokholm, Michaela; Hegelund, Josefine Nymark; Ladegård, Anne Hald; Schjoerring, Jan Kofod; Husted, Søren

2014-01-01

Many metabolic processes in plants are regulated by manganese (Mn) but limited information is available on the molecular mechanisms controlling cellular Mn homeostasis. In this study, a yeast assay was used to isolate and characterize two genes, MTP8.1 and MTP8.2, which encode membrane-bound proteins belonging to the cation diffusion facilitator (CDF) family in the cereal species barley (Hordeum vulgare). Transient expression in onion epidermal cells showed that MTP8.1 and MTP8.2 proteins fused to the green fluorescent protein (GFP) are localized to Golgi. When heterologously expressed in yeast, MTP8.1 and MTP8.2 were found to be Mn transporters catalysing Mn efflux in a similar manner as the Golgi localized endogenous yeast protein Pmr1p. The level of MTP8.1 transcripts in barley roots increased with external Mn supply ranging from deficiency to toxicity, while MTP8.2 transcripts decreased under the same conditions, indicating non-overlapping functions for the two genes. In barley leaves, the expression of both MTP8 genes declined in response to toxic Mn additions to the roots suggesting a role in ensuring proper delivery of Mn to Golgi. Based on the above we suggest that barley MTP8 proteins are involved in Mn loading to the Golgi apparatus and play a role in Mn homeostasis by delivering Mn to Mn-dependent enzymes and/or by facilitating Mn efflux via secretory vesicles. This study highlights the importance of MTP transporters in Mn homeostasis and is the first report of Golgi localized Mn2+ transport proteins in a monocot plant species. PMID:25486417

Cation trapping by cellular acidic compartments: Beyond the concept of lysosomotropic drugs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Marceau, François, E-mail: francois.marceau@crchul.ulaval.ca; Bawolak, Marie-Thérèse; Lodge, Robert

“Lysosomotropic” cationic drugs are known to concentrate in acidic cell compartments due to low retro-diffusion of the protonated molecule (ion trapping); they draw water by an osmotic mechanism, leading to a vacuolar response. Several aspects of this phenomenon were recently reexamined. (1) The proton pump vacuolar (V)-ATPase is the driving force of cationic drug uptake and ensuing vacuolization. In quantitative transport experiments, V-ATPase inhibitors, such as bafilomycin A1, greatly reduced the uptake of cationic drugs and released them in preloaded cells. (2) Pigmented or fluorescent amines are effectively present in a concentrated form in the large vacuoles. (3) Consistent withmore » V-ATPase expression in trans-Golgi, lysosomes and endosomes, a fraction of the vacuoles is consistently labeled with trans-Golgi markers and protein secretion and endocytosis are often inhibited in vacuolar cells. (4) Macroautophagic signaling (accumulation of lipidated and membrane-bound LC3 II) and labeling of the large vacuoles by the autophagy effector LC3 were consistently observed in cells, precisely at incubation periods and amine concentrations that cause vacuolization. Vacuoles also exhibit late endosome/lysosome markers, because they may originate from such organelles or because macroautophagosomes fuse with lysosomes. Autophagosome persistence is likely due to the lack of resolution of autophagy, rather than to nutritional deprivation. (5) Increased lipophilicity decreases the threshold concentration for the vacuolar and autophagic cytopathology, because simple diffusion into cells is limiting. (6) A still unexplained mitotic arrest is consistently observed in cells loaded with amines. An extended recognition of relevant clinical situations is proposed for local or systemic drug administration.« less

Role of cations as components of jelly coats in Bufo arenarum fertilization.

PubMed

Medina, Marcela Fátima; Crespo, Claudia Alejandra; Ramos, Inés; Fernández, Silvia Nélida

2010-02-01

The role of monovalent (Na+, K+) and divalent (Ca2+, Mg2+) cations in Bufo arenarum fertilization was analysed. Our results showed that the highest fertilization percentages were obtained when strings of uterine oocytes (UO) were inseminated. Under these conditions, full jelly (FJ), which represents the jelly coats surrounding the oocytes at the time of deposition, contained 68.5 +/- 7.0 mM Na+, 27.4 +/- 2.4 mM K+, 6.3 +/- 0.9 mM Ca2+ and 6.9 +/- 0.9 mM Mg2+. When the strings of oocytes were washed in deionized water, these cations diffused into the liquid medium surrounding them. There was a marked similarity between the loss of Ca2+ in the jelly and the decrease in the fertilizability of the UO. Furthermore, the use of chelating agents of divalent cations showed the importance of the Ca2+ contained in the jelly. When Ca2+ was sequestered from the jelly coats by the addition of the chelating agents to the insemination medium as well as by pretreatment of the UO strings, a decrease in fertilization percentages occurred, this effect being dose dependent and more marked with EGTA. These results demonstrate that the Ca2+ in the jelly plays a role in fertilization. Nevertheless, taking into account that during the washing of the jelly other jelly coat components were diffused and considering that the addition of Ca2+ to the insemination medium reverted significantly, but only partially, the loss of fertilizability of jellied UO (washed), the participation of other components in the fertilization mechanism is suggested.

Influence of cations on noncovalent interactions between 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and dissolved fulvic and humic acids.

PubMed

Gadad, Praveen; Nanny, Mark A

2008-12-01

The influence of cations (Na(+), Ca(2+) and Mg(2+)) on noncovalent interactions between 6-propionyl-2-dimethylaminonaphthalene (PRODAN) and dissolved fulvic acids (FAs) (Norman landfill leachate fulvic acid (NLFA) and Suwannee River fulvic acid (SRFA)) and dissolved humic acids (HAs) (Suwannee River humic acid (SRHA) and Leonardite humic acid (LHA)) was examined using steady-state fluorescence spectroscopy at pH 4, 7 and 10 as a function of cation concentration (up to 25-100mM). Regardless of pH and cation concentration, PRODAN quenching by FA was unaffected by cations. However, interactions between PRODAN and HA decreased in the presence of cations at pH 7 and 10. Cation concentrations below the HA charge density resulted in the greatest decrease of PRODAN quenching, while very little additional decrease in PRODAN quenching occurred at cation concentrations above the HA charge density. This suggests that as the HA carboxylic acid functional groups form inner sphere complexes with divalent cations, intramolecular interactions result in a contraction of the HA molecular structure, thereby preventing PRODAN from associating with the condensed aromatic, electron accepting moieties inherent within HA molecules and responsible for PRODAN quenching. However, once the HA carboxylic acid functional groups are fully titrated with divalent cations, PRODAN quenching is no longer significantly influenced by the further addition of cations, even though these additional cations facilitate intermolecular interactions between the HA molecules to form supramolecular HA aggregates that can continue to increase in size. Regardless of FA and HA type, pH, cation type and concentration, the lack of blue-shifted fluorescence emission spectra indicated that micelle-like hydrophobic regions, amenable to PRODAN partitioning, were not formed by intra- and intermolecular interactions of FA and HA.

Thermodynamics of binding interactions between extracellular polymeric substances and heavy metals by isothermal titration microcalorimetry.

PubMed

Yan, Peng; Xia, Jia-Shuai; Chen, You-Peng; Liu, Zhi-Ping; Guo, Jin-Song; Shen, Yu; Zhang, Cheng-Cheng; Wang, Jing

2017-05-01

Extracellular polymeric substances (EPS) play a crucial role in heavy metal bio-adsorption using activated sludge, but the interaction mechanism between heavy metals and EPS remains unclear. Isothermal titration calorimetry was employed to illuminate the mechanism in this study. The results indicate that binding between heavy metals and EPS is spontaneous and driven mainly by enthalpy change. Extracellular proteins in EPS are major participants in the binding process. Environmental conditions have significant impact on the adsorption performance. Divalent and trivalent cations severely impeded the binding of heavy metal ions to EPS. Electrostatic interaction mainly attributed to competition between divalent cations and heavy metal ions; trivalent cations directly competed with heavy metal ions for EPS binding sites. Trivalent cations were more competitive than divalent cations for heavy metal ion binding because they formed complexing bonds. This study facilitates a better understanding about the interaction between heavy metals and EPS in wastewater treatment. Copyright © 2017 Elsevier Ltd. All rights reserved.

Determination of the zincate diffusion coefficient and its application to alkaline battery problems

NASA Technical Reports Server (NTRS)

May, C. E.; Kautz, Harold E.

1978-01-01

The diffusion coefficient for the zincate ion at 24 C was found to be 9.9 X 10 to the minus 7th power squared cm per sec + or - 30 percent in 45 percent potassium hydroxide and 1.4 x 10 to the minus 7 squared cm per sec + or - 25 percent in 40 percent sodium hydroxide. Comparison of these values with literature values at different potassium hydroxide concentrations show that the Stokes-Einstein equation is obeyed. The diffusion coefficient is characteristic of the zincate ion (not the cation) and independent of its concentration. Calculations with the measured value of the diffusion coefficient show that the zinc concentration in an alkaline zincate half cell becomes uniform throughout in tens of hours by diffusion alone. Diffusion equations are derived which are applicable to finite size chambers. Details and discussion of the experimental method are also given.

Determination of the zincate diffusion coefficient and its application to alkaline battery problems

NASA Technical Reports Server (NTRS)

May, C. E.; Kautz, H. E.

1978-01-01

The diffusion coefficient for the zincate ion at 24 C was found to be 9.9 x 10 to the -7th power sq cm/sec + or - 30% in 45% potassium hydroxide and 1.4 x 10 to the -7th power sq cm/sec + or - 25% in 40% sodium hydroxide. Comparison of these values with literature values at different potassium hydroxide concentrations show that the Stokes-Einstein equation is obeyed. The diffusion coefficient is characteristic of the zincate ion (not the cation) and independent of its concentration. Calculations with the measured value of the diffusion coefficient show that the zinc concentration in an alkaline zincate half-cell becomes uniform throughout in tens of hours by diffusion alone. Diffusion equations are derived which are applicable to finite-size chambers. Details and discussion of the experimental method are also given.

Electronic Absorption Spectra of Mass-Selected Hydrocarbon Cations in Solid Neon: C_nH_4+ (n=5-8,10,12)

NASA Astrophysics Data System (ADS)

Nagy, A.; Fulara, J.; Garkusha, I.; Maier, J. P.

2011-05-01

Small, unsaturated hydrocarbons, C_nH_m (n,m≤6), play an important role in astrochemical models as they have been detected in various space objects such as the interstellar medium or envelopes of carbon-rich stars. Although identification of most of these species was based on rotational studies, they are candidate carriers of the infamous diffuse interstellar bands. It has been proposed that corresponding cationic species formed upon UV radiation may also be of astrophysical relevance; therefore, their optical spectra need to be determined. In this contribution, electronic absorption spectra of mass-selected C_nH_4+ (n=5-8,10,12) ions trapped in neon matrices are presented. The cations were produced in a hot-cathode discharge source, guided through a series of electrostatic lenses, mass filtered and co-deposited with excess of neon onto a rhodium-coated sapphire plate held at 6 K. In the same experiments, neutral species were generated from the cations by a photobleaching procedure.

Novel pH-Sensitive Cationic Lipids with Linear Ortho Ester Linkers for Gene Delivery

PubMed Central

Chen, Haigang; Zhang, Huizhen; Thor, Der; Rahimian, Roshanak; Guo, Xin

2012-01-01

In an effort to develop pH-sensitive lipoplexes for efficient gene delivery, we report three novel cationic lipids containing a linear ortho ester linker that conjugates either the headgroup (Type I) or one hydrocarbon chain (Type II) with the rest of the lipid molecule. The cationic lipids carry either an iodide or a chloride counterion. Compared to our previously reported cyclic ortho ester linker, the linear ortho ester linker facilitated the construction of cationic liposomes and lipoplexes with different helper lipids. The chloride counterion not only facilitated the hydration of the lipid films during liposome construction, but also enhanced the hydrolysis of the ortho ester linker in the lipoplexes. After incubation at endosomal pH 5.5, the Type I lipoplexes aggregated and destabilized the endosome-mimicking model liposomes, but not the Type II lipoplexes. The helper lipids (DOPE or cholesterol) of the lipoplexes enhanced the pH-sensitivity of the Type I lipoplexes. In CV-1 cells (monkey kidney fibroblast), the Type I ortho ester-based lipoplexes, especially those with the chloride counterion, significantly improved the gene transfection efficiency, in some cases by more than 100 fold, compared to their pH-insensitive counterparts consisting of DOTAP. The gene transfection efficiency of the ortho ester-based lipoplexes was well correlated with their rate of aggregation and membrane destabilization in response to the endosomal pH 5.5. PMID:22480493

Density-Functional-Theory Modeling of Cation Diffusion in Bulk La 1 - x Sr x MnO 3 ± δ ( x = 0.0 – 0.25 ) for Solid-Oxide Fuel-Cell Cathodes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Yueh-Lin; Duan, Yuhua; Morgan, Dane

In this work, the A - and B -site cation migration pathways involving defect complexes in bulk La 1-xSr xMnO 3±δ (LSM) at x = 0.0-0.25 are investigated based on density-functional-theory modeling for solid-oxide fuel-cell (SOFC) cathode applications. We propose a dominant A -site cation migration mechanism which involves an A -site cation (e.g., Lamore » $$x\\atop{A}$$) V A"' of a V A"' -V B"' cluster, where La$$x\\atop{A}$$, V A"' and V B"' are La 3+, A-site vacancy, and B-site vacancy in bulk LSM, respectively, and V A"' -V B"' is the first nearest-neighbor V A"' and V B"' pair. This hop exhibits an approximately 1.6-eV migration barrier as compared to approximately 2.9 eV of the La$$x\\atop{A}$$ hop into a V A"'. This decrease in the cation migration barrier is attributed to the presence of the V B"' relieving the electrostatic repulsion and steric constraints to the migrating A-site cations in the transition-state image configurations.« less

Density-Functional-Theory Modeling of Cation Diffusion in Bulk La 1 - x Sr x MnO 3 ± δ ( x = 0.0 – 0.25 ) for Solid-Oxide Fuel-Cell Cathodes

DOE PAGES

Lee, Yueh-Lin; Duan, Yuhua; Morgan, Dane; ...

2017-10-04

In this work, the A - and B -site cation migration pathways involving defect complexes in bulk La 1-xSr xMnO 3±δ (LSM) at x = 0.0-0.25 are investigated based on density-functional-theory modeling for solid-oxide fuel-cell (SOFC) cathode applications. We propose a dominant A -site cation migration mechanism which involves an A -site cation (e.g., Lamore » $$x\\atop{A}$$) V A"' of a V A"' -V B"' cluster, where La$$x\\atop{A}$$, V A"' and V B"' are La 3+, A-site vacancy, and B-site vacancy in bulk LSM, respectively, and V A"' -V B"' is the first nearest-neighbor V A"' and V B"' pair. This hop exhibits an approximately 1.6-eV migration barrier as compared to approximately 2.9 eV of the La$$x\\atop{A}$$ hop into a V A"'. This decrease in the cation migration barrier is attributed to the presence of the V B"' relieving the electrostatic repulsion and steric constraints to the migrating A-site cations in the transition-state image configurations.« less

Visualizing the kinetic power stroke that drives proton-coupled Zn(II) transport

PubMed Central

Gupta, Sayan; Chai, Jin; Cheng, Jie; D'Mello, Rhijuta; Chance, Mark R.; Fu, Dax

2014-01-01

The proton gradient is a principal energy source for respiration-dependent active transport, but the structural mechanisms of proton-coupled transport processes are poorly understood. YiiP is a proton-coupled zinc transporter found in the cytoplasmic membrane of E. coli, and the transport-site of YiiP receives protons from water molecules that gain access to its hydrophobic environment and transduces the energy of an inward proton gradient to drive Zn(II) efflux1,2. This membrane protein is a well characterized member3-7 of the protein family of cation diffusion facilitators (CDFs) that occurs at all phylogenetic levels8-10. X-ray mediated hydroxyl radical labeling of YiiP and mass spectrometric analysis showed that Zn(II) binding triggered a highly localized, all-or-none change of water accessibility to the transport-site and an adjacent hydrophobic gate. Millisecond time-resolved dynamics revealed a concerted and reciprocal pattern of accessibility changes along a transmembrane helix, suggesting a rigid-body helical reorientation linked to Zn(II) binding that triggers the closing of the hydrophobic gate. The gated water access to the transport-site enables a stationary proton gradient to facilitate the conversion of zinc binding energy to the kinetic power stroke of a vectorial zinc transport. The kinetic details provide energetic insights into a proton-coupled active transport reaction. PMID:25043033

DOE Office of Scientific and Technical Information (OSTI.GOV)

Emin, David, E-mail: emin@unm.edu; Akhtari, Massoud; Ellingson, B. M.

We analyze the transient-dc and frequency-dependent electrical conductivities between blocking electrodes. We extend this analysis to measurements of ions’ transport in freshly excised bulk samples of human brain tissue whose complex cellular structure produces blockages. The associated ionic charge-carrier density and diffusivity are consistent with local values for sodium cations determined non-invasively in brain tissue by MRI (NMR) and diffusion-MRI (spin-echo NMR). The characteristic separation between blockages, about 450 microns, is very much shorter than that found for sodium-doped gel proxies for brain tissue, >1 cm.

Structure and dynamics of solvated polyethylenimine chains

NASA Astrophysics Data System (ADS)

Beu, Titus A.; Farcaş, Alexandra

2017-12-01

Polimeric gene-delivery carriers have attracted great interest in recent years, owing to their applicability in gene therapy. In particular, cationic polymers represent the most promising delivery vectors for nucleic acids into the cells. This study presents extensive atomistic molecular dynamics simulations of linear polyethylenimine chains. The simulations show that the variation of the chain size and protonation fraction causes a substantial change of the diffusion coefficient. Examination of the solvated chains suggests the possibility of controlling the polymer diffusion mobility in solution.

The Diffusion Process of Patient Education in Dutch Community Pharmacy: An Exploration.

ERIC Educational Resources Information Center

Pronk, M. C. M.; Blom, A. Th. G.; Van Burg, A.; Jonkers, R.

2001-01-01

Identifies barriers and facilitators to the implementation of patient education in community pharmacies and classifies these barriers and facilitators into the diffusion stages of Rogers'"Innovations in Organizations" model. Discusses the implementation of patient education activities that require individual and organizational change in…

Mechanism of Facilitated Diffusion during a DNA Search in Crowded Environments.

PubMed

Krepel, Dana; Gomez, David; Klumpp, Stefan; Levy, Yaakov

2016-11-03

The key feature explaining the rapid recognition of a DNA target site by its protein lies in the combination of one- and three-dimensional (1D and 3D) diffusion, which allows efficient scanning of the many alternative sites. This facilitated diffusion mechanism is expected to be affected by cellular conditions, particularly crowding, given that up to 40% of the total cellular volume may by occupied by macromolecules. Using coarse-grained molecular dynamics and Monte Carlo simulations, we show that the crowding particles can enhance facilitated diffusion and accelerate search kinetics. This effect originates from a trade-off between 3D and 1D diffusion. The 3D diffusion coefficient is lower under crowded conditions, but it has little influence because the excluded volume effect of molecular crowding restricts its use. Largely prevented from using 3D diffusion, the searching protein dramatically increases its use of the hopping search mode, which results in a higher linear diffusion coefficient. The coefficient of linear diffusion also increases under crowded conditions as a result of increased collisions between the crowding particles and the searching protein. Overall, less 3D diffusion coupled with an increase in the use of the hopping and speed of 1D diffusion results in faster search kinetics under crowded conditions. Our study shows that the search kinetics and mechanism are modulated not only by the crowding occupancy but also by the properties of the crowding particles and the salt concentration.

Interplay of electrostatics and lipid packing determines the binding of charged polymer coated nanoparticles to model membranes.

PubMed

Biswas, Nupur; Bhattacharya, Rupak; Saha, Arindam; Jana, Nikhil R; Basu, Jaydeep K

2015-10-07

Understanding of nanoparticle-membrane interactions is useful for various applications of nanoparticles like drug delivery and imaging. Here we report on the studies of interaction between hydrophilic charged polymer coated semiconductor quantum dot nanoparticles with model lipid membranes. Atomic force microscopy and X-ray reflectivity measurements suggest that cationic nanoparticles bind and penetrate bilayers of zwitterionic lipids. Penetration and binding depend on the extent of lipid packing and result in the disruption of the lipid bilayer accompanied by enhanced lipid diffusion. On the other hand, anionic nanoparticles show minimal membrane binding although, curiously, their interaction leads to reduction in lipid diffusivity. It is suggested that the enhanced binding of cationic QDs at higher lipid packing can be understood in terms of the effective surface potential of the bilayers which is tunable through membrane lipid packing. Our results bring forth the subtle interplay of membrane lipid packing and electrostatics which determine nanoparticle binding and penetration of model membranes with further implications for real cell membranes.

Aquaporin-facilitated transmembrane diffusion of hydrogen peroxide.

PubMed

Bienert, Gerd P; Chaumont, François

2014-05-01

Hydrogen peroxide (H2O2) is an important signaling compound that has recently been identified as a new substrate for several members of the aquaporin superfamily in various organisms. Evidence is emerging about the physiological significance of aquaporin-facilitated H2O2 diffusion. This review summarizes current knowledge about aquaporin-facilitated H2O2 diffusion across cellular membranes. It focuses on physicochemical and experimental evidence demonstrating the involvement of aquaporins in the transport of this redox signaling compound and discusses the regulation and structural prerequisites of these channels to transmit this signal. It also provides perspectives about the potential importance of aquaporin-facilitated H2O2 diffusion processes and places this knowledge in the context of the current understanding of transmembrane redox signaling processes. Specific aquaporin isoforms facilitate the passive diffusion of H2O2 across biological membranes and control H2O2 membrane permeability and signaling in living organisms. Redox signaling is a very important process regulating the physiology of cells and organisms in a similar way to the well-characterized hormonal and calcium signaling pathways. Efficient transmembrane diffusion of H2O2, a key molecule in the redox signaling network, requires aquaporins and makes these channels important players in this signaling process. Channel-mediated membrane transport allows the fine adjustment of H2O2 levels in the cytoplasm, intracellular organelles, the apoplast, and the extracellular space, which are essential for it to function as a signal molecule. This article is part of a Special Issue entitled Aquaporins. © 2013.

Differential Microscopic Mobility of Components within a Deep Eutectic Solvent

DOE PAGES

Wagle, Durgesh V.; Baker, Gary A.; Mamontov, Eugene

2015-07-13

From macroscopic measurements of deep eutectic solvents such as glyceline (1:2 molar ratio of choline chloride to glycerol), the long-range translational diffusion of the larger cation (choline) is known to be slower compared to that of the smaller hydrogen bond donor (glycerol). However, when the diffusion dynamics are analyzed on the subnanometer length scale, we discover that the displacements associated with the localized diffusive motions are actually larger for choline. This counterintuitive diffusive behavior can be understood as follows. The localized diffusive motions confined in the transient cage of neighbor particles, which precede the cage-breaking long-range diffusion jumps, are moremore » spatially constrained for glycerol than for choline because of the stronger hydrogen bonds the former makes with chloride anions. The implications of differential localized mobility of the constituents should be especially important for applications where deep eutectic solvents are confined on the nanometer length scale and their long-range translational diffusion is strongly inhibited (e.g., within microporous media).« less

Detection of Buckminsterfullerene emission in the diffuse interstellar medium.

PubMed

Berné, O; Cox, N L J; Mulas, G; Joblin, C

2017-09-01

Emission of fullerenes in their infrared vibrational bands has been detected in space near hot stars. The proposed attribution of the diffuse interstellar bands at 9577 and 9632 Å to electronic transitions of the buckminsterfullerene cation (i.e. [Formula: see text]) was recently supported by new laboratory data, confirming the presence of this species in the diffuse interstellar medium (ISM). In this letter, we present the detection, also in the diffuse ISM, of the 17.4 and 18.9 μ m emission bands commonly attributed to vibrational bands of neutral C 60 . According to classical models that compute the charge state of large molecules in space, C 60 is expected to be mostly neutral in the diffuse ISM. This is in agreement with the abundances of diffuse C 60 we derive here from observations. We also find that C 60 is less abundant in the diffuse ISM than in star-forming regions, supporting the theory that C 60 can be formed in these regions.

Post-Synthetic Modification of Porphyrin-Encapsulating Metal-Organic Materials by Cooperative Addition of Inorganic Salts to Enhance CO 2/CH 4 Selectivity

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Zhenjie; Gao, Wen-Yang; Wojtas, Lukasz

Keeping MOM: Reaction of biphenyl-3,4',5-tricarboxylate and Cd(NO 3) 2 in the presence of meso-tetra(N-methyl-4-pyridyl)porphine tetratosylate afforded porph@MOM-11, a microporous metal–organic material (MOM) that encapsulates cationic porphyrins and solvent in alternating open channels. Porph@MOM-11 has cation and anion binding sites that facilitate cooperative addition of inorganic salts (such as M +Cl -) in a stoichiometric fashion.

Surface hopping investigation of the relaxation dynamics in radical cations

DOE PAGES

Assmann, Mariana; Weinacht, Thomas; Matsika, Spiridoula

2016-01-19

Ionization processes can lead to the formation of radical cations with population in several ionic states. In this study, we examine the dynamics of three radical cations starting from an excited ionic state using trajectory surface hopping dynamics in combination with multiconfigurational electronic structure methods. The efficiency of relaxation to the ground state is examined in an effort to understand better whether fragmentation of cations is likely to occur directly on excited states or after relaxation to the ground state. The results on cyclohexadiene, hexatriene, and uracil indicate that relaxation to the ground ionic state is very fast in thesemore » systems, while fragmentation before relaxation is rare. Ultrafast relaxation is facilitated by the close proximity of electronic states and the presence of two- and three-state conical intersections. Furthermore, examining the properties of the systems in the Franck-Condon region can give some insight into the subsequent dynamics.« less

Mesoporous nanocrystalline film architecture for capacitive storage devices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dunn, Bruce S.; Tolbert, Sarah H.; Wang, John

A mesoporous, nanocrystalline, metal oxide construct particularly suited for capacitive energy storage that has an architecture with short diffusion path lengths and large surface areas and a method for production are provided. Energy density is substantially increased without compromising the capacitive charge storage kinetics and electrode demonstrates long term cycling stability. Charge storage devices with electrodes using the construct can use three different charge storage mechanisms immersed in an electrolyte: (1) cations can be stored in a thin double layer at the electrode/electrolyte interface (non-faradaic mechanism); (2) cations can interact with the bulk of an electroactive material which then undergoesmore » a redox reaction or phase change, as in conventional batteries (faradaic mechanism); or (3) cations can electrochemically adsorb onto the surface of a material through charge transfer processes (faradaic mechanism).« less

Examination of the nature of lattice matched III V semiconductor interfaces using computer simulated molecular beam epitaxial growth I. AC/BC interfaces

NASA Astrophysics Data System (ADS)

Thomsen, M.; Ghaisas, S. V.; Madhukar, A.

1987-07-01

A previously developed computer simulation of molecular beam epitaxial growth of III-V semiconductors based on the configuration dependent reactive incorporation (CDRI) model is extended to allow for two different cation species. Attention is focussed on examining the nature of interfaces formed in lattice matched quantum well structures of the form AC/BC/AC(100). We consider cation species with substantially different effective diffusion lengths, as is the case with Al and Ga during the growth of their respective As compounds. The degree of intermixing occuring at the interface is seen to be dependent upon, among other growth parameters, the pressure of the group V species during growth. Examination of an intraplanar order parameter at the interfaces reveals the existence of short range clustering of the cation species.

Facilitated Diffusion of Transcription Factor Proteins with Anomalous Bulk Diffusion.

PubMed

Liu, Lin; Cherstvy, Andrey G; Metzler, Ralf

2017-02-16

What are the physical laws of the diffusive search of proteins for their specific binding sites on DNA in the presence of the macromolecular crowding in cells? We performed extensive computer simulations to elucidate the protein target search on DNA. The novel feature is the viscoelastic non-Brownian protein bulk diffusion recently observed experimentally. We examine the influence of the protein-DNA binding affinity and the anomalous diffusion exponent on the target search time. In all cases an optimal search time is found. The relative contribution of intermittent three-dimensional bulk diffusion and one-dimensional sliding of proteins along the DNA is quantified. Our results are discussed in the light of recent single molecule tracking experiments, aiming at a better understanding of the influence of anomalous kinetics of proteins on the facilitated diffusion mechanism.

Cucumber metal transport protein MTP8 confers increased tolerance to manganese when expressed in yeast and Arabidopsis thaliana

PubMed Central

Migocka, Magdalena; Papierniak, Anna; Maciaszczyk-Dziubińska, Ewa; Poździk, Piotr; Posyniak, Ewelina; Garbiec, Arnold; Filleur, Sophie

2014-01-01

Cation diffusion facilitator (CDF) proteins are ubiquitous divalent cation transporters that have been proved to be essential for metal homeostasis and tolerance in Archaebacteria, Bacteria, and Eukaryota. In plants, CDFs are designated as metal tolerance proteins (MTPs). Due to the lack of genomic resources, studies on MTPs in other plants, including cultivated crops, are lacking. Here, the identification and organization of genes encoding members of the MTP family in cucumber are described. The first functional characterization of a cucumber gene encoding a member of the Mn-CDF subgroup of CDF proteins, designated as CsMTP8 based on the highest homology to plant MTP8, is also presented. The expression of CsMTP8 in Saccharomyces cerevisiae led to increased Mn accumulation in yeast cells and fully restored the growth of mutants hypersensitive to Mn in Mn excess. Similarly, the overexpression of CsMTP8 in Arabidopsis thaliana enhanced plant tolerance to high Mn in nutrition media as well as the accumulation of Mn in plant tissues. When fused to green fluorescent protein (GFP), CsMTP8 localized to the vacuolar membranes in yeast cells and to Arabidopsis protoplasts. In cucumber, CsMTP8 was expressed almost exclusively in roots, and the level of gene transcript was markedly up-regulated or reduced under elevated Mn or Mn deficiency, respectively. Taken together, the results suggest that CsMTP8 is an Mn transporter localized in the vacuolar membrane, which participates in the maintenance of Mn homeostasis in cucumber root cells. PMID:25039075

Tumor-targeted pH/redox dual-sensitive unimolecular nanoparticles for efficient siRNA delivery.

PubMed

Chen, Guojun; Wang, Yuyuan; Xie, Ruosen; Gong, Shaoqin

2017-08-10

A unique pH/redox dual-sensitive cationic unimolecular nanoparticle (NP) enabling excellent endosomal/lysosomal escape and efficient siRNA decomplexation inside the target cells was developed for tumor-targeted delivery of siRNA. siRNA was complexed into the cationic core of the unimolecular NP through electrostatic interactions. The cationic core used for complexing siRNA contained reducible disulfide bonds that underwent intracellular reduction owing to the presence of high concentrations of reduced glutathione (GSH) inside the cells, thereby facilitating the decomplexation of siRNA from the unimolecular NPs. The cationic polymers were conjugated onto the hyperbranched core (H40) via a pH-sensitive bond, which further facilitated the decomplexation of siRNA from the NPs. In vitro studies on the siRNA release behaviors showed that dual stimuli (pH=5.3, 10mM GSH) induced the quickest release of siRNA from the NPs. In addition, the imidazole groups attached to the cationic polymer segments enhanced the endosomal/lysosomal escape of NPs via the proton sponge effect. Intracellular tracking studies revealed that siRNA delivered by unimolecular NPs was efficiently released to the cytosol. Moreover, the GE11 peptide, an anti-EGFR peptide, enhanced the cellular uptake of NPs in MDA-MB-468, an EFGR-overexpressing triple negative breast cancer (TNBC) cell line. The GE11-conjugated, GFP-siRNA-complexed NPs exhibited excellent GFP gene silencing efficiency in GFP-MDA-MB-468 TNBC cells without any significant cytotoxicity. Therefore, these studies suggest that this smart unimolecular NP could be a promising nanoplatform for targeted siRNA delivery to EFGR-overexpressing cancer cells. Copyright © 2017 Elsevier B.V. All rights reserved.

Study of quantitative interactions of potato and corn starch granules with ions in diluted solutions of heavy metal salts.

PubMed

Szymońska, Joanna; Molenda, Marcin; Wieczorek, Jerzy

2015-12-10

Interactions of potato and corn starch granules with ions in diluted solutions of silver, lead, copper or iron salts were investigated. It was shown experimentally that granules accumulated the cations in amounts depending on the granule structure and water content as well as a type of both metal and counter-ions present in solution. Potato starch retained almost three times more cations compared to corn starch what was proportional to the total phosphorous content in these starches. Quantity of milligrams of cations bound by 1g of starch was inversely correlated with the cation hydration. Ag(+), Pb(2+) and Cu(2+) were connected in stoichiometric amounts of moles to semicrystalline and amorphous parts of the granules. Fe(3+) ions were accumulated in higher than stoichiometric quantities mainly in granule amorphous regions. Metal ions penetrated into granules together with anions except nitrates which remained on surface of potato starch granules. Cations facilitated the starch thermal decomposition in accordance with values of their standard redox potentials. Nitrates supported this process only in the presence of base metal cations. Copyright © 2015 Elsevier Ltd. All rights reserved.

Kinetics of intercalation of fluorescent probes in magnesium–aluminium layered double hydroxide within a multiscale reaction–diffusion framework

PubMed Central

Saliba, Daniel

2016-01-01

We report the synthesis of magnesium–aluminium layered double hydroxide (LDH) using a reaction–diffusion framework (RDF) that exploits the multiscale coupling of molecular diffusion with chemical reactions, nucleation and growth of crystals. In an RDF, the hydroxide anions are allowed to diffuse into an organic gel matrix containing the salt mixture needed for the precipitation of the LDH. The chemical structure and composition of the synthesized magnesium–aluminium LDHs are determined using powder X-ray diffraction (PXRD), thermo-gravimetric analysis, differential scanning calorimetry, solid-state nuclear magnetic resonance (SSNMR), Fourier transform infrared and energy dispersive X-ray spectroscopy. This novel technique also allows the investigation of the mechanism of intercalation of some fluorescent probes, such as the neutral three-dimensional rhodamine B (RhB) and the negatively charged two-dimensional 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS), using in situ steady-state fluorescence spectroscopy. The incorporation of these organic dyes inside the interlayer region of the LDH is confirmed via fluorescence microscopy, solid-state lifetime, SSNMR and PXRD. The activation energies of intercalation of the corresponding molecules (RhB and HPTS) are computed and exhibit dependence on the geometry of the involved probe (two or three dimensions), the charge of the fluorescent molecule (anionic, cationic or neutral) and the cationic ratio of the corresponding LDH. This article is part of the themed issue ‘Multiscale modelling at the physics–chemistry–biology interface’. PMID:27698034

Transport of water and ions in partially water-saturated porous media. Part 2. Filtration effects

NASA Astrophysics Data System (ADS)

Revil, A.

2017-05-01

A new set of constitutive equations describing the transport of the ions and water through charged porous media and considering the effect of ion filtration is applied to the problem of reverse osmosis and diffusion of a salt. Starting with the constitutive equations derived in Paper 1, I first determine specific formula for the osmotic coefficient and effective diffusion coefficient of a binary symmetric 1:1 salt (such as KCl or NaCl) as a function of a dimensionless number Θ corresponding to the ratio between the cation exchange capacity (CEC) and the salinity. The modeling is first carried with the Donnan model used to describe the concentrations of the charge carriers in the pore water phase. Then a new model is developed in the thin double layer approximation to determine these concentrations. These models provide explicit relationships between the concentration of the ionic species in the pore space and those in a neutral reservoir in local equilibrium with the pore space and the CEC. The case of reverse osmosis and diffusion coefficient are analyzed in details for the case of saturated and partially saturated porous materials. Comparisons are done with experimental data from the literature obtained on bentonite. The model predicts correctly the influence of salinity (including membrane behavior at high salinities), porosity, cation type (K+ versus Na+), and water saturation on the osmotic coefficient. It also correctly predicts the dependence of the diffusion coefficient of the salt with the salinity.

Kinetics of intercalation of fluorescent probes in magnesium-aluminium layered double hydroxide within a multiscale reaction-diffusion framework

NASA Astrophysics Data System (ADS)

Saliba, Daniel; Al-Ghoul, Mazen

2016-11-01

We report the synthesis of magnesium-aluminium layered double hydroxide (LDH) using a reaction-diffusion framework (RDF) that exploits the multiscale coupling of molecular diffusion with chemical reactions, nucleation and growth of crystals. In an RDF, the hydroxide anions are allowed to diffuse into an organic gel matrix containing the salt mixture needed for the precipitation of the LDH. The chemical structure and composition of the synthesized magnesium-aluminium LDHs are determined using powder X-ray diffraction (PXRD), thermo-gravimetric analysis, differential scanning calorimetry, solid-state nuclear magnetic resonance (SSNMR), Fourier transform infrared and energy dispersive X-ray spectroscopy. This novel technique also allows the investigation of the mechanism of intercalation of some fluorescent probes, such as the neutral three-dimensional rhodamine B (RhB) and the negatively charged two-dimensional 8-hydroxypyrene-1,3,6-trisulfonic acid (HPTS), using in situ steady-state fluorescence spectroscopy. The incorporation of these organic dyes inside the interlayer region of the LDH is confirmed via fluorescence microscopy, solid-state lifetime, SSNMR and PXRD. The activation energies of intercalation of the corresponding molecules (RhB and HPTS) are computed and exhibit dependence on the geometry of the involved probe (two or three dimensions), the charge of the fluorescent molecule (anionic, cationic or neutral) and the cationic ratio of the corresponding LDH. This article is part of the themed issue 'Multiscale modelling at the physics-chemistry-biology interface'.

Transient cerebral hypoperfusion assisted intraarterial cationic liposome delivery to brain tissue

PubMed Central

Joshi, Shailendra; Singh-Moon, Rajinder P.; Wang, Mei; Chaudhuri, Durba B.; Holcomb, Mark; Straubinger, Ninfa L.; Bruce, Jeffrey N.; Bigio, Irving J.; Straubinger, Robert M.

2014-01-01

Object Transient cerebral hypoperfusion (TCH) has empirically been used to assist intraarterial (IA) drug delivery to brain tumors. Transient (< 3 min) reduction of cerebral blood flow (CBF) occurs during many neuro- and cardiovascular interventions and has recently been used to better target IA drugs to brain tumors. In the present experiments, we assessed whether the effectiveness of IA delivery of cationic liposomes could be improved by TCH. Methods Cationic liposomes composed of 1:1 DOTAP:PC (dioleoyl-trimethylammonium-propane:phosphatidylcholine) were administered to three groups of Sprague Dawley rats. In the first group, we tested the effect of blood flow reduction on IA delivery of cationic liposomes. In the second group, we compared TCH-assisted IA liposomal delivery vs. intravenous (IV) administration of the same dose. In the third group, we assessed retention of cationic liposomes in brain four hours after TCH assisted delivery. The liposomes contained a near infrared dye, DilC18(7), whose concentration could be measured in vivo by diffuse reflectance spectroscopy. Results IA injections of cationic liposomes during TCH increased their delivery approximately four-fold compared to injections during normal blood flow. Optical pharmacokinetic measurements revealed that relative to IV injections, IA injection of cationic liposomes during TCH produced tissue concentrations that were 100-fold greater. The cationic liposomes were retained in the brain tissue four hours after a single IA injection. There was no gross impairment of neurological functions in surviving animals. Conclusions Transient reduction in CBF significantly increased IA delivery of cationic liposomes in the brain. High concentrations of liposomes could be delivered to brain tissue after IA injections with concurrent TCH while none could be detected after IV injection. IA-TCH injections were well tolerated and cationic liposomes were retained for at least 4 hours after IA administration. These results should encourage development of cationic liposomal formulations of chemotherapeutic drugs and their IA delivery during TCH. PMID:24664370

Topotactic Metal-Insulator Transition in Epitaxial SrFeO x Thin Films

DOE PAGES

Khare, Amit; Shin, Dongwon; Yoo, Tae Sup; ...

2017-07-31

Multivalent transition metal oxides provide fascinating and rich physics related to oxygen stoichiometry. In particular, the adoptability of various valence states of transition metals enables perovskite oxides to display mixed (oxygen) ionic and electronic conduction and catalytic activity useful in many practical applications, including solid-oxide fuel cells (SOFCs), rechargeable batteries, gas sensors, and memristive devices. For proper realization of the ionic conduction and catalytic activity, it is essential to understand the reversible oxidation and reduction process, which is governed by oxygen storage/release steps in oxides. Topotactic phase transformation facilitates the redox process in perovskites with specific oxygen vacancy ordering bymore » largely varying the oxygen concentration of a material without losing the lattice framework. The concentration and diffusion of oxide ions (O 2–), the valence state of the transition metal cations, and the thermodynamic structural integrity together provide fundamental understanding and ways to explicitly control the redox reaction.[6] In addition, it offers an attractive route for tuning the emergent physical properties of transition metal oxides, via strong coupling between the crystal lattice and electronic structure.« less

Transport, electrochemical and thermophysical properties of two N-donor-functionalised ionic liquids.

PubMed

Rüther, Thomas; Harris, Kenneth R; Horne, Michael D; Kanakubo, Mitsuhiro; Rodopoulos, Theo; Veder, Jean-Pierre; Woolf, Lawrence A

2013-12-23

Two N-donor-functionalised ionic liquids (ILs), 1-ethyl-1,4-dimethylpiperazinium bis(trifluoromethylsulfonyl)amide (1) and 1-(2-dimethylaminoethyl)-dimethylethylammonium bis(trifluoromethylsulfonyl)amide (2), were synthesised and their electrochemical and transport properties measured. The data were compared with the benchmark system, N-butyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (3). Marked differences in thermal and electrochemical stability were observed between the two tertiary-amine-functionalised salts and the non-functionalised benchmark. The former are up to 170 K and 2 V less stable than the structural counterpart lacking a tertiary amine function. The ion self-diffusion coefficients (Di ) and molar conductivities (Λ) are higher for the IL with an open-chain cation (2) than that with a cyclic cation (1), but less than that with a non-functionalised, heterocyclic cation (3). The viscosities (η) show the opposite behaviour. The Walden [Λ[proportionality](1/η)(t) ] and Stokes-Einstein [Di /T)[proportionality](1/η)(t) ] exponents, t, are very similar for the three salts, 0.93-0.98 (±0.05); that is, the self-diffusion coefficients and conductivity are set by η. The Di for 1 and 2 are the same, within experimental error, at the same viscosity, whereas Λ for 1 is approximately 13% higher than that of 2. The diffusion and molar conductivity data are consistent, with a slope of 0.98±0.05 for a plot of ln(ΛT) against ln(D+ +D- ). The Nernst-Einstein deviation parameters (Δ) are such that the mean of the two like-ion VCCs is greater than that of the unlike ions. The values of Δ are 0.31, 0.36 and 0.42 for 3, 1 and 2, respectively, as is typical for ILs, but there is some subtlety in the ion interactions given 2 has the largest value. The distinct diffusion coefficients (DDC) follow the order D(d)__ < D(d)++ < D(d)+_, as is common for [Tf2N](-) salts. The ion motions are not correlated as in an electrolyte solution: instead, there is greater anti-correlation between the velocities of a given anion and the overall ensemble of anions in comparison to those for the cationic analogue, the anti-correlation for the velocities of which is in turn greater than that for a given ion and the ensemble of oppositely charged ions, an observation that is due to the requirement for the conservation of momentum in the system. The DDC also show fractional SE behaviour with t~0.95. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Competitive separation of di- vs. mono-valent cations in electrodialysis: effects of the boundary layer properties.

PubMed

Kim, Younggy; Walker, W Shane; Lawler, Desmond F

2012-05-01

In electrodialysis desalination, the boundary layer near ion-exchange membranes is the limiting region for the overall rate of ionic separation due to concentration polarization over tens of micrometers in that layer. Under high current conditions, this sharp concentration gradient, creating substantial ionic diffusion, can drive a preferential separation for certain ions depending on their concentration and diffusivity in the solution. Thus, this study tested a hypothesis that the boundary layer affects the competitive transport between di- and mono-valent cations, which is known to be governed primarily by the partitioning with cation-exchange membranes. A laboratory-scale electrodialyzer was operated at steady state with a mixture of 10mM KCl and 10mM CaCl(2) at various flow rates. Increased flows increased the relative calcium transport. A two-dimensional model was built with analytical solutions of the Nernst-Planck equation. In the model, the boundary layer thickness was considered as a random variable defined with three statistical parameters: mean, standard deviation, and correlation coefficient between the thicknesses of the two boundary layers facing across a spacer. Model simulations with the Monte Carlo method found that a greater calcium separation was achieved with a smaller mean, greater standard deviation, or more negative correlation coefficient. The model and experimental results were compared for the cationic transport number as well as the current and potential relationship. The mean boundary layer thickness was found to decrease from 40 to less than 10 μm as the superficial water velocity increased from 1.06 to 4.24 cm/s. The standard deviation was greater than the mean thickness at slower water velocities and smaller at faster water velocities. Copyright © 2012 Elsevier Ltd. All rights reserved.

Investigation of Dynamics in BMIM TFSA Ionic Liquid through Variable Temperature and Pressure NMR Relaxometry and Diffusometry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pilar, Kartik; Rua, Armando; Suarez, Sophia N.

A comprehensive variable temperature, pressure and frequency multinuclear ( 1H, 2H, and 19F) magnetic resonance study was undertaken on selectively deuterated 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (BMIM TFSA) ionic liquid isotopologues. This study builds on our earlier investigation of the effects of increasing alkyl chain length on diffusion and dynamics in imidazolium-based TFSA ionic liquids. Fast field cycling 1H T 1 data revealed multiple modes of motion. Through calculation of diffusion coefficient (D) values and activation energies, the low- and high-field regimes were assigned to the translational and reorientation dynamics respectively. Variable-pressure 2H T 1 measurements reveal site-dependent interactions in the cation withmore » strengths in the order MD 3 > CD 3 > CD 2, indicating dissimilarities in the electric field gradients along the alkyl chain, with the CD 2 sites having the largest gradient. Additionally, the α saturation effect in T 1 vs. P was observed for all three sites, suggesting significant reduction of the short-range rapid reorientational dynamics. This reduction was also deduced from the variable pressure 1H T 1 data, which showed an approach to saturation for both the methyl and butyl group terminal methyl sites. Pressure-dependent D measurements show independent motions for both cations and anions, with the cations having greater D values over the entire pressure range.« less

The bundling of actin with polyethylene glycol 8000 in the presence and absence of gelsolin.

PubMed Central

Goverman, J; Schick, L A; Newman, J

1996-01-01

Actin filament and bundle formation occur in the cytosol under conditions of very high total macromolecular concentration. In this study we have utilized the inert molecule polyethylene glycol 8000 (PEG) as a means of simulating crowded conditions in vitro. Column-purified Ca-actin was polymerized in the absence and presence of gelsolin (to regulate mean filament lengths between 50 and 5000 mers) and PEG (2-8%) using various concentrations of KCl and/or 2 mM divalent cations. Bundling was characterized by the scattered light intensity and mean diffusion coefficients obtained from dynamic light scattering, as well as by fluorescence and phase-contrast microscopy. The minimum concentration of KCl required for bundling decreases both with increasing concentration of PEG at a fixed mean filament length, and with decreasing filament length at a fixed concentration of PEG. In the absence of divalent cation, bundling is reversible on dilution, as determined by intensity levels, diffusion coefficients, and microscopy. However, with either 2 mM Mg2+ or Ca2+ added, bundling is irreversible under conditions of higher PEG concentrations or longer filaments, indicating that osmotic pressure effects cannot fully explain actin bundling with PEG. Weaker divalent cation-binding sites on actin as well as disulfide bonds appear to be involved in the irreversible bundling. Images FIGURE 7 PMID:8874022

Investigation of Dynamics in BMIM TFSA Ionic Liquid through Variable Temperature and Pressure NMR Relaxometry and Diffusometry

DOE PAGES

Pilar, Kartik; Rua, Armando; Suarez, Sophia N.; ...

2017-05-11

A comprehensive variable temperature, pressure and frequency multinuclear ( 1H, 2H, and 19F) magnetic resonance study was undertaken on selectively deuterated 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide (BMIM TFSA) ionic liquid isotopologues. This study builds on our earlier investigation of the effects of increasing alkyl chain length on diffusion and dynamics in imidazolium-based TFSA ionic liquids. Fast field cycling 1H T 1 data revealed multiple modes of motion. Through calculation of diffusion coefficient (D) values and activation energies, the low- and high-field regimes were assigned to the translational and reorientation dynamics respectively. Variable-pressure 2H T 1 measurements reveal site-dependent interactions in the cation withmore » strengths in the order MD 3 > CD 3 > CD 2, indicating dissimilarities in the electric field gradients along the alkyl chain, with the CD 2 sites having the largest gradient. Additionally, the α saturation effect in T 1 vs. P was observed for all three sites, suggesting significant reduction of the short-range rapid reorientational dynamics. This reduction was also deduced from the variable pressure 1H T 1 data, which showed an approach to saturation for both the methyl and butyl group terminal methyl sites. Pressure-dependent D measurements show independent motions for both cations and anions, with the cations having greater D values over the entire pressure range.« less

CATAPHORETIC CHARGES OF COLLODION PARTICLES AND ANOMALOUS OSMOSIS THROUGH COLLODION MEMBRANES FREE FROM PROTEIN

PubMed Central

Loeb, Jacques

1922-01-01

1. It had been shown in previous papers that when a salt solution is separated from pure water by a collodion membrane, water diffuses through the membrane as if it were positively charged and as if it were attracted by the anion of the salt in solution and repelled by the cation with a force increasing with the valency. In this paper, measurements of the P.D. across the membrane (E) are given, showing that when an electrical effect is added to the purely osmotic effect of the salt solution in the transport of water from the side of pure water to the solution, the latter possesses a considerable negative charge which increases with increasing valency of the anion of the salt and diminishes with increasing valency of the cation. It is also shown that a similar valency effect exists in the diffusion potentials between salt solutions and pure water without the interposition of a membrane. 2. This makes it probable that the driving force for the electrical transport of water from the side of pure water into solution is primarily a diffusion potential. 3. It is shown that the hydrogen ion concentration of the solution affects the transport curves and the diffusion potentials in a similar way. 4. It is shown, however, that the diffusion potential without interposition of the membrane differs in a definite sense from the P.D. across the membrane and that therefore the P.D. across the membrane (E) is a modified diffusion potential. 5. Measurements of the P.D. between collodion particles and aqueous solutions (ε) were made by the method of cataphoresis, which prove that water in contact with collodion particles free from protein practically always assumes a positive charge (except in the presence of salts with trivalent and probably tetravalent cations of a sufficiently high concentration). 6. It is shown that an electrical transport of water from the side of water into the solution is always superposed upon the osmotic transport when the sign of charge of the solution in the potential across the membrane (E) is opposite to that of the water in the P.D. between collodion particle and water (ε); supporting the theoretical deductions made by Bartell. 7. It is shown that the product of the P.D. across the membrane (E) into the cataphoretic P.D. between collodion particles and aqueous solution (ε) accounts in general semiquantitatively for that part of the transport of water into the solution which is due to the electrical forces responsible for anomalous osmosis. PMID:19871981

Determination of diffusion coefficients of various livestock antibiotics in water at infinite dilution

NASA Astrophysics Data System (ADS)

Soriano, Allan N.; Adamos, Kristoni G.; Bonifacio, Pauline B.; Adornado, Adonis P.; Bungay, Vergel C.; Vairavan, Rajendaran

2017-11-01

The fate of antibiotics entering the environment raised concerns on the possible effect of antimicrobial resistance bacteria. Prediction of the fate and transport of these particles are needed to be determined, significantly the diffusion coefficient of antibiotic in water at infinite dilution. A systematic determination of diffusion coefficient of antibiotic in water at infinite dilution of five different kinds of livestock antibiotics namely: Amtyl, Ciprotyl, Doxylak Forte, Trisullak, and Vetracin Gold in the 293.15 to 313.15 K temperature range are reported through the use of the method involving the electrolytic conductivity measurements. A continuous stirred tank reactor is utilized to measure the electrolytic conductivities of the considered systems. These conductivities are correlated by using the Nernst-Haskell equation to determine the infinite dilution diffusion coefficient. Determined diffusion coefficients are based on the assumption that in dilute solution, these antibiotics behave as strong electrolyte from which H+ cation dissociate from the antibiotic's anion.

Anomalous cation diffusion in salt-doped confined bilayer ice.

PubMed

Qiu, Hu; Xue, Minmin; Shen, Chun; Guo, Wanlin

2018-05-17

The diffusive dynamics of aqueous electrolyte solutions in nanoconfined spaces has attracted considerable attention due to their potential applications in desalination, biosensors and supercapacitors. Here we show by molecular dynamics simulations that lithium and sodium ions diffuse at a rate at least an order of magnitude higher than that of water molecules when the ions are trapped in an ice bilayer confined between two parallel plates. This novel picture is in sharp contrast to the prevailing view that the diffusion rate of ions is comparable to or even lower than that of water in both bulk and confined solutions. The predicted high ion mobility stems from frequent lateral hopping of ions along the coordination sites inside the hydrogen-bonding network connecting the two water layers of the ice bilayer. This anomalous diffusion should provide new insights into the physics of confined aqueous electrolytes.

Garnet zoning and metamorphism of the Barrovian type area, Scotland

NASA Astrophysics Data System (ADS)

Dempster, T. J.

1985-03-01

A microprobe investigation of the high grade metamorphic zones from the Barrovian type area in Angus, Scotland, shows the importance of local zones of retrograde cation exchange between garnet, staurolite and biotite. The interpretation of this zoning, established during a slow cooling history, is critical to any study of metamorphic reactions or conditions. The extent and intensity of these diffusion effects are dependent on a number of parameters including grainsize, fabric orientation, heating and cooling history, and the modal abundance of the phases. Increasing diffusion within garnets with metamorphic grade, and the subsequent retrograde effects are modelled using Temperature-Time-Transformation diagrams and provide information on the activation energy for Fe-Mg diffusion in garnet.

A Cation-containing Polymer Anion Exchange Membrane based on Poly(norbornene)

NASA Astrophysics Data System (ADS)

Beyer, Frederick; Price, Samuel; Ren, Xiaoming; Savage, Alice

Cation-containing polymers are being studied widely for use as anion exchange membranes (AEMs) in alkaline fuel cells (AFCs) because AEMs offer a number of potential benefits including allowing a solid state device and elimination of the carbonate poisoning problem. The successful AEM will combine high performance from several orthogonal properties, having robust mechanical strength even when wet, high hydroxide conductivity, and the high chemical stability required for long device lifetimes. In this study, we have synthesized a model cationic polymer that combines three of the key advantages of Nafion. The polymer backbone based on semicrystalline atactic poly(norbornene) offers good mechanical properties. A flexible, ether-based tether between the backbone and fixed cation charged species (quaternary ammonium) should provide the low-Tg, hydrophilic environment required to facilitate OH- transport. Finally, methyl groups have been added at the beta position relative to the quaternary ammonium cation to prevent Hoffman elimination, one mechanism by which AEMs are neutralized in a high pH environment. In this poster, we will present our findings on mechanical properties, morphology, charge transport, and chemical stability of this material.

Surface coating of siRNA-peptidomimetic nano-self-assemblies with anionic lipid bilayers: enhanced gene silencing and reduced adverse effects in vitro

NASA Astrophysics Data System (ADS)

Zeng, Xianghui; de Groot, Anne Marit; Sijts, Alice J. A. M.; Broere, Femke; Oude Blenke, Erik; Colombo, Stefano; van Eden, Willem; Franzyk, Henrik; Nielsen, Hanne Mørck; Foged, Camilla

2015-11-01

Cationic vectors have demonstrated the potential to facilitate intracellular delivery of therapeutic oligonucleotides. However, enhanced transfection efficiency is usually associated with adverse effects, which also proves to be a challenge for vectors based on cationic peptides. In this study a series of proteolytically stable palmitoylated α-peptide/β-peptoid peptidomimetics with a systematically varied number of repeating lysine and homoarginine residues was shown to self-assemble with small interfering RNA (siRNA). The resulting well-defined nanocomplexes were coated with anionic lipids giving rise to net anionic liposomes. These complexes and the corresponding liposomes were optimized towards efficient gene silencing and low adverse effects. The optimal anionic liposomes mediated a high silencing effect, which was comparable to that of the control (cationic Lipofectamine 2000), and did not display any noticeable cytotoxicity and immunogenicity in vitro. In contrast, the corresponding nanocomplexes mediated a reduced silencing effect with a more narrow safety window. The surface coating with anionic lipid bilayers led to partial decomplexation of the siRNA-peptidomimetic nanocomplex core of the liposomes, which facilitated siRNA release. Additionally, the optimal anionic liposomes showed efficient intracellular uptake and endosomal escape. Therefore, these findings suggest that a more efficacious and safe formulation can be achieved by surface coating of the siRNA-peptidomimetic nano-self-assemblies with anionic lipid bilayers.Cationic vectors have demonstrated the potential to facilitate intracellular delivery of therapeutic oligonucleotides. However, enhanced transfection efficiency is usually associated with adverse effects, which also proves to be a challenge for vectors based on cationic peptides. In this study a series of proteolytically stable palmitoylated α-peptide/β-peptoid peptidomimetics with a systematically varied number of repeating lysine and homoarginine residues was shown to self-assemble with small interfering RNA (siRNA). The resulting well-defined nanocomplexes were coated with anionic lipids giving rise to net anionic liposomes. These complexes and the corresponding liposomes were optimized towards efficient gene silencing and low adverse effects. The optimal anionic liposomes mediated a high silencing effect, which was comparable to that of the control (cationic Lipofectamine 2000), and did not display any noticeable cytotoxicity and immunogenicity in vitro. In contrast, the corresponding nanocomplexes mediated a reduced silencing effect with a more narrow safety window. The surface coating with anionic lipid bilayers led to partial decomplexation of the siRNA-peptidomimetic nanocomplex core of the liposomes, which facilitated siRNA release. Additionally, the optimal anionic liposomes showed efficient intracellular uptake and endosomal escape. Therefore, these findings suggest that a more efficacious and safe formulation can be achieved by surface coating of the siRNA-peptidomimetic nano-self-assemblies with anionic lipid bilayers. Electronic supplementary information (ESI) available: Non-fusogenic liposomes; cytotoxicity of naked siRNA and the empty vector; immunogenicity; low-magnification images; DOPE/DPPC liposomes. See DOI: 10.1039/c5nr04807a

Ion Dynamics in a Mixed-Cation Alkoxy-Ammonium Ionic Liquid Electrolyte for Sodium Device Applications.

PubMed

Pope, Cameron R; Kar, Mega; MacFarlane, Douglas R; Armand, Michel; Forsyth, Maria; O'Dell, Luke A

2016-10-18

The ion dynamics in a novel sodium-containing room-temperature ionic liquid (IL) consisting of an ether-functionalised quaternary ammonium cation and bis(trifluoromethylsulfonyl)amide [NTf 2 ] anion with various concentrations of Na[NTf 2 ] have been characterised using differential scanning calorimetry, impedance spectroscopy, diffusometry and NMR relaxation measurements. The IL studied has been specifically designed to dissolve a relatively large concentration of Na[NTf 2 ] salt (over 2 mol kg -1 ) as this has been shown to improve ion transport and conductivity. Consistent with other studies, the measured ionic conductivity and diffusion coefficients show that the overall ionic mobility decreases with decreasing temperature and increasing salt content. NMR relaxation measurements provide evidence for correlated dynamics between the ether-functionalised ammonium and Na cations, possibly with the latter species acting as cross-links between multiple ammonium cations. Finally, preliminary cyclic voltammetry experiments show that this IL can undergo stable electrochemical cycling and could therefore be potentially useful as an electrolyte in a Na-based device. © 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Human proximal tubule epithelial cells cultured on hollow fibers: living membranes that actively transport organic cations

PubMed Central

Jansen, J.; De Napoli, I. E; Fedecostante, M.; Schophuizen, C. M. S.; Chevtchik, N. V.; Wilmer, M. J.; van Asbeck, A. H.; Croes, H. J.; Pertijs, J. C.; Wetzels, J. F. M.; Hilbrands, L. B.; van den Heuvel, L. P.; Hoenderop, J. G.; Stamatialis, D.; Masereeuw, R.

2015-01-01

The bioartificial kidney (BAK) aims at improving dialysis by developing ‘living membranes’ for cells-aided removal of uremic metabolites. Here, unique human conditionally immortalized proximal tubule epithelial cell (ciPTEC) monolayers were cultured on biofunctionalized MicroPES (polyethersulfone) hollow fiber membranes (HFM) and functionally tested using microfluidics. Tight monolayer formation was demonstrated by abundant zonula occludens-1 (ZO-1) protein expression along the tight junctions of matured ciPTEC on HFM. A clear barrier function of the monolayer was confirmed by limited diffusion of FITC-inulin. The activity of the organic cation transporter 2 (OCT2) in ciPTEC was evaluated in real-time using a perfusion system by confocal microscopy using 4-(4-(dimethylamino)styryl)-N-methylpyridinium iodide (ASP+) as a fluorescent substrate. Initial ASP+ uptake was inhibited by a cationic uremic metabolites mixture and by the histamine H2-receptor antagonist, cimetidine. In conclusion, a ‘living membrane’ of renal epithelial cells on MicroPES HFM with demonstrated active organic cation transport was successfully established as a first step in BAK engineering. PMID:26567716

Oxygen diffusion in Gd-doped mixed oxides

DOE PAGES

Galvin, C. O. T.; Cooper, M. W. D.; Rushton, M. J. D.; ...

2017-10-23

Molecular dynamics simulations have been performed to investigate oxygen transport in (U xPu x-1) 0.95Gd 0.05O 1.975, (U xTh x-1) 0.95Gd 0.05O 1.975 and (Pu xTh x-1) 0.95Gd 0.05O 1.975 between 1000 and 3200 K. Oxygen diffusivity and corresponding activation energies are examined and compared to values for the undoped (U xPu x-1)O 2, (U xTh x-1)O 2 and (Pu xTh x-1)O 2 systems where compositions between end members display enhanced diffusivity. Below the superionic transition oxygen diffusivity for the Gd doped systems is orders of magnitude greater compared to their undoped counterparts. But, enhanced diffusivity for doped mixed actinidemore » cation compositions is not observed compared to doped end members. Furthermore, changes in activation energy suggest changes in diffusion regime, which correspond to the creation of thermally activated oxygen defects.« less

Oxygen diffusion in Gd-doped mixed oxides

DOE Office of Scientific and Technical Information (OSTI.GOV)

Galvin, C. O. T.; Cooper, M. W. D.; Rushton, M. J. D.

Molecular dynamics simulations have been performed to investigate oxygen transport in (U xPu x-1) 0.95Gd 0.05O 1.975, (U xTh x-1) 0.95Gd 0.05O 1.975 and (Pu xTh x-1) 0.95Gd 0.05O 1.975 between 1000 and 3200 K. Oxygen diffusivity and corresponding activation energies are examined and compared to values for the undoped (U xPu x-1)O 2, (U xTh x-1)O 2 and (Pu xTh x-1)O 2 systems where compositions between end members display enhanced diffusivity. Below the superionic transition oxygen diffusivity for the Gd doped systems is orders of magnitude greater compared to their undoped counterparts. But, enhanced diffusivity for doped mixed actinidemore » cation compositions is not observed compared to doped end members. Furthermore, changes in activation energy suggest changes in diffusion regime, which correspond to the creation of thermally activated oxygen defects.« less

[PAH Cations as Viable Carriers of DIBs

NASA Technical Reports Server (NTRS)

Snow, Ted

1998-01-01

This report is intended to fill in the blanks in NASA's file system for our lab astro study of molecular ions of astrophysical interest. In order to give NASA what it needs for its files, I attach below the text of the section from our recent proposal to continue this work, in which we describe progress to date, including a large number of publications. Our initial studies were focused on PAH cations, which appear to be viable candidates as the carriers of the DIBs, an idea that has been supported by laboratory spectroscopy of PAH cations in inert matrices. Beginning with the simplest aromatic (benzene; C6H6) and moving progressively to larger species (naphthalene, C10OH8; pyrene, C16H10; and most recently chrysene, C18H12), we have been able to derive rate coefficients for reactions with neutral spices that are abundant in the diffuse interstellar medium.

Antimicrobial agent-free hybrid cationic starch/sodium alginate polyelectrolyte films for food packaging materials.

PubMed

Şen, Ferhat; Uzunsoy, İrem; Baştürk, Emre; Kahraman, Memet Vezir

2017-08-15

This study aimed to develop polyelectrolyte structured antimicrobial food packaging materials that do not contain any antimicrobial agents. Cationic starch was synthesized and characterized by FT-IR spectroscopy and 1 H NMR spectroscopy. Its nitrogen content was determined by Kjeldahl method. Polyelectrolyte structured antimicrobial food packaging materials were prepared using starch, cationic starch and sodium alginate. Antimicrobial activity of materials was defined by inhibition zone method (disc diffusion method). Thermal stability of samples was evaluated by TGA and DSC. Hydrophobicity of samples was determined by contact angle measurements. Surface morphology of samples was investigated by SEM. Moreover, gel contents of samples were determined. The obtained results prove that produced food packaging materials have good thermal, antimicrobial and surface properties, and they can be used as food packaging material in many industries. Copyright © 2017 Elsevier Ltd. All rights reserved.

Lipid and cationic polymer based transduction of botulinum holotoxin, or toxin protease alone, extends the target cell range and improves the efficiency of intoxication.

PubMed

Kuo, Chueh-Ling; Oyler, George; Shoemaker, Charles B

2010-01-01

Botulinum neurotoxin (BoNT) heavy chain (Hc) facilitates receptor-mediated endocytosis into neuronal cells and transport of the light chain (Lc) protease to the cytosol where neurotransmission is inhibited as a result of SNARE protein cleavage. Here we show that the role of BoNT Hc in cell intoxication can be replaced by commercial lipid-based and polycationic polymer DNA transfection reagents. BoNT "transduction" by these reagents permits efficient intoxication of neuronal cells as well as some non-neuronal cell lines normally refractory to BoNT. Surprisingly, the reagents facilitate delivery of recombinant BoNT Lc protease to the cytosol of both neuronal and non-neuronal cells in the absence of BoNT Hc, and with sensitivities approaching that of BoNT holotoxin. Transduction of BoNT, as with natural intoxication, is inhibited by bafilomycin A1, methylamine and ammonium chloride indicating that both pathways require endosome acidification. DNA transfection reagents facilitate intoxication by holotoxins, or isolated Lc proteases, of all three BoNT serotypes tested (A, B, E). These results suggest that lipid and cationic polymer transfection reagents facilitate cytosolic delivery of BoNT holotoxins and isolated Lc proteases by an endosomal uptake pathway.

Lipid and cationic polymer based transduction of botulinum holotoxin, or toxin protease alone, extends the target cell range and improves the efficiency of intoxication

PubMed Central

Kuo, Chueh-Ling; Oyler, George; Shoemaker, Charles B.

2009-01-01

Botulinum neurotoxin (BoNT) heavy chain (Hc) facilitates receptor-mediated endocytosis into neuronal cells and transport of the light chain (Lc) protease to the cytosol where neurotransmission is inhibited as a result of SNARE protein cleavage. Here we show that the role of BoNT Hc in cell intoxication can be replaced by commercial lipid-based and polycationic polymer DNA transfection reagents. BoNT “transduction” by these reagents permits efficient intoxication of neuronal cells as well as some non-neuronal cell lines normally refractory to BoNT. Surprisingly, the reagents facilitate delivery of recombinant BoNT Lc protease to the cytosol of both neuronal and non-neuronal cells in the absence of BoNT Hc, and with sensitivities approaching that of BoNT holotoxin. Transduction of BoNT, as with natural intoxication, is inhibited by bafilomycin A1, methylamine and ammonium chloride indicating that both pathways require endosome acidification. DNA transfection reagents facilitate intoxication by holotoxins, or isolated Lc proteases, of all three BoNT serotypes tested (A, B, E). These results suggest that lipid and cationic polymer transfection reagents facilitate cytosolic delivery of BoNT holotoxins and isolated Lc proteases by an endosomal uptake pathway. PMID:19852976

Peptides containing antigenic and cationic domains have enhanced, multivalent immunogenicity when bound to DNA vaccines.

PubMed

Riedl, Petra; Reimann, Jörg; Schirmbeck, Reinhold

2004-02-01

We explored strategies to codeliver DNA- and peptide-based vaccines in a way that enhances the immunogenicity of both components of the combination vaccine for T cells. Specific CD8(+) T cell responses to an antigenic peptide are primed when the peptide is fused to a cationic peptide domain that is bound to plasmid DNA or oligonucleotides (ODN; with or without CpG motifs). Plasmid DNA mixed with antigenic/cationic peptides or histones forms large complexes with different biological properties depending on the molar ratios of peptide/protein and polynucleotide. Complexes containing high (but not low) molar ratios of cationic peptide to DNA facilitate transfection (DNA uptake and expression of the plasmid-encoded product) of cells. In contrast, complexes containing low (but not high) molar ratios of cationic peptide to DNA prime potent multispecific T cell responses after a single intramuscular injection of the complexes. The general validity of this observation was confirmed mixing different antigenic/cationic peptides with different DNA vaccines. In these vaccine formulations, multispecific CD8(+) T cell responses specific for epitopes of the peptide- as well as the DNA-based vaccine were efficiently coprimed, together with humoral antibody responses to conformational determinants of large viral antigens encoded by the DNA vaccine. The data indicate that mixtures of DNA vaccines with antigenic, cationic peptides are immunogenic vaccine formulations particularly suited for the induction of multispecific T cell responses.

Increased Degree of Unsaturation in the Lipid of Antifungal Cationic Amphiphiles Facilitates Selective Fungal Cell Disruption.

PubMed

Steinbuch, Kfir B; Benhamou, Raphael I; Levin, Lotan; Stein, Reuven; Fridman, Micha

2018-05-11

Antimicrobial cationic amphiphiles derived from aminoglycosides act through cell membrane permeabilization but have limited selectivity for microbial cell membranes. Herein, we report that an increased degree of unsaturation in the fatty acid segment of antifungal cationic amphiphiles derived from the aminoglycoside tobramycin significantly reduced toxicity to mammalian cells. A collection of tobramycin-derived cationic amphiphiles substituted with C 18 lipid chains varying in degree of unsaturation and double bond configuration were synthesized. All had potent activity against a panel of important fungal pathogens including strains with resistance to a variety of antifungal drugs. The tobramycin-derived cationic amphiphile substituted with linolenic acid with three cis double bonds (compound 6) was up to an order of magnitude less toxic to mammalian cells than cationic amphiphiles composed of lipids with a lower degree of unsaturation and than the fungal membrane disrupting drug amphotericin B. Compound 6 was 12-fold more selective (red blood cell hemolysis relative to antifungal activity) than compound 1, the derivative with a fully saturated lipid chain. Notably, compound 6 disrupted the membranes of fungal cells without affecting the viability of cocultured mammalian cells. This study demonstrates that the degree of unsaturation and the configuration of the double bond in lipids of cationic amphiphiles are important parameters that, if optimized, result in compounds with broad spectrum and potent antifungal activity as well as reduced toxicity toward mammalian cells.

Tunnel Structured α-MnO 2 with Different Tunnel Cations (H + , K + , Ag + ) as Cathode Materials in Rechargeable Lithium Batteries: The Role of Tunnel Cation on Electrochemistry

DOE PAGES

Poyraz, Altug S.; Huang, Jianping; Cheng, Shaobo; ...

2017-07-12

α-MnO 2 type manganese dioxide is an interesting prospective cathode material for reversible lithium insertion owing to its cation accessible tunnels (0.46nm x 0.46nm), high voltage, and low cost. The tunneled structure is synthetically formed by the assistance of cations acting as structure directing agents where the cations may remain in the tunnel. The electrochemistry of this family of materials is strongly dependent on the morphological and physicochemical (i.e. surface area, crystallite size, and average manganese oxidation state) properties as well as tunnel occupancy. For this work, we prepared a set of materials Mn 8O 16·0.81H 2O, K 0.81Mn 8Omore » 16·0.78H 2O and Ag 1.33Mn 8O 16·0.95H 2O with similar nanorod morphology, crystallite size, surface area, and tunnel water content. This set of samples allowed us to investigate the role of tunnel cations in the electrochemistry of α-MnO 2 type manganese dioxide in a lithium based environment while minimizing the effects of the other parameters. The electrochemistry was evaluated using cyclic voltammetry, galvanostatic cycling, rate capability, and galvanostatic intermittent titration type testing. Mn 8O 16·0.81H 2O showed higher loaded voltages, improved capacity retention, and higher specific energy relative to K 0.81Mn 8O 16·0.78H 2O and Ag 1.33Mn 8O 16·0.95H 2O. After 100 cycles, Mn 8O 16·0.81H 2O delivered ~200% more capacity than Ag 1.33Mn 8O 16·0.95H 2O (64 vs. 129 mAh/g) and ~35% more capacity than K 0.81Mn 8O 16·0.78H 2O (85 vs. 129 mAh/g). Mn 8O 16·0.81H 2O also showed higher effective lithium diffusion coefficients (DLi+) and higher rate capability compared to K 0.81Mn 8O 16·0.78H 2O and Ag 1.33Mn 8O 16·0.95H 2O suggesting faster Li+ ion diffusion in the absence of large metal tunnel cations.« less

Tunnel Structured α-MnO 2 with Different Tunnel Cations (H + , K + , Ag + ) as Cathode Materials in Rechargeable Lithium Batteries: The Role of Tunnel Cation on Electrochemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Poyraz, Altug S.; Huang, Jianping; Cheng, Shaobo

α-MnO 2 type manganese dioxide is an interesting prospective cathode material for reversible lithium insertion owing to its cation accessible tunnels (0.46nm x 0.46nm), high voltage, and low cost. The tunneled structure is synthetically formed by the assistance of cations acting as structure directing agents where the cations may remain in the tunnel. The electrochemistry of this family of materials is strongly dependent on the morphological and physicochemical (i.e. surface area, crystallite size, and average manganese oxidation state) properties as well as tunnel occupancy. For this work, we prepared a set of materials Mn 8O 16·0.81H 2O, K 0.81Mn 8Omore » 16·0.78H 2O and Ag 1.33Mn 8O 16·0.95H 2O with similar nanorod morphology, crystallite size, surface area, and tunnel water content. This set of samples allowed us to investigate the role of tunnel cations in the electrochemistry of α-MnO 2 type manganese dioxide in a lithium based environment while minimizing the effects of the other parameters. The electrochemistry was evaluated using cyclic voltammetry, galvanostatic cycling, rate capability, and galvanostatic intermittent titration type testing. Mn 8O 16·0.81H 2O showed higher loaded voltages, improved capacity retention, and higher specific energy relative to K 0.81Mn 8O 16·0.78H 2O and Ag 1.33Mn 8O 16·0.95H 2O. After 100 cycles, Mn 8O 16·0.81H 2O delivered ~200% more capacity than Ag 1.33Mn 8O 16·0.95H 2O (64 vs. 129 mAh/g) and ~35% more capacity than K 0.81Mn 8O 16·0.78H 2O (85 vs. 129 mAh/g). Mn 8O 16·0.81H 2O also showed higher effective lithium diffusion coefficients (DLi+) and higher rate capability compared to K 0.81Mn 8O 16·0.78H 2O and Ag 1.33Mn 8O 16·0.95H 2O suggesting faster Li+ ion diffusion in the absence of large metal tunnel cations.« less

Misfit strain driven cation inter-diffusion across an epitaxial multiferroic thin film interface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sankara Rama Krishnan, P. S.; Munroe, Paul; Nagarajan, V.

Cation intermixing at functional oxide interfaces remains a highly controversial area directly relevant to interface-driven nanoelectronic device properties. Here, we systematically explore the cation intermixing in epitaxial (001) oriented multiferroic bismuth ferrite (BFO) grown on a (001) lanthanum aluminate (LAO) substrate. Aberration corrected dedicated scanning transmission electron microscopy and electron energy loss spectroscopy reveal that the interface is not chemically sharp, but with an intermixing of ∼2 nm. The driving force for this process is identified as misfit-driven elastic strain. Landau-Ginzburg-Devonshire-based phenomenological theory was combined with the Sheldon and Shenoy formula in order to understand the influence of boundary conditions andmore » depolarizing fields arising from misfit strain between the LAO substrate and BFO film. The theory predicts the presence of a strong potential gradient at the interface, which decays on moving into the bulk of the film. This potential gradient is significant enough to drive the cation migration across the interface, thereby mitigating the misfit strain. Our results offer new insights on how chemical roughening at oxide interfaces can be effective in stabilizing the structural integrity of the interface without the need for misfit dislocations. These findings offer a general formalism for understanding cation intermixing at highly strained oxide interfaces that are used in nanoelectronic devices.« less

The effect of various electrolyte cations on electrochemical performance of polypyrrole/RGO based supercapacitors.

PubMed

Zhu, Jianbo; Xu, Youlong; Wang, Jie; Lin, Jun; Sun, Xiaofei; Mao, Shengchun

2015-11-21

In this work, polypyrrole/graphene doped by p-toluenesulfonic is prepared as an active material for supercapacitors, and its capacitance performance is investigated in various aqueous electrolytes including HCl, LiCl, NaCl, and KCl with a concentration of 3 M, respectively. A rising trend of capacitance is observed according to the cationic mobility (Li(+) < Na(+) < K(+) < H(+)), which is due to its effect on the ionic conductivity, efficient ion/charge diffusion/exchange and relaxation time. On the other hand, long-term cycling stability is in the following order: KCl < NaCl < LiCl < HCl, corresponding to the decreasing tendency of cation size (K(+) > Na(+) > Li(+) > H(+)). The reason can be attributed to the fact that the insertion/de-insertion of large size cation brings a significant doping level decrease and an over-oxidation increase during the charging-discharging cycles. Hence, we not only obtain good capacitance performance (280.3 F g(-1) at 5 mV s(-1)), superior rate capability (225.8 F g(-1) at 500 mV s(-1)) and high cycling stability (92.0% capacitance retention after 10,000 cycles at 1 A g(-1)) by employing 3 M HCl as an electrolyte, but also reveal that the electrolyte cations have a significant effect on the supercapacitors' electrochemical performance.

Mechanism of Enhancement of Virus Plaques by Cationic Polymers

PubMed Central

Wallis, Craig; Melnick, Joseph L.

1968-01-01

It has been assumed that plaque enhancement by cationic polymers is due to their binding of sulfated polysaccharides in agar. However, viruses that are enhanced by cationic polymers, diethylaminoethyl-dextran, and protamine were found not to be inhibited by polyanions in agar under the usual overlay conditions. In the case of adenovirus, enhancement by protamine seems to be due to the protamine serving as a source of arginine; enzymes released from the cultured cells digest the protamine and provide a reservoir of arginine for the cells. Other viruses (herpes and echovirus types 3, 4, 5, and 6) known to be susceptible to agar inhibitors were found to be enhanced by cationic polymers even under starch gel and methylcellulose overlays, which are free of polyanions. Since cationic polymers enhance the diffusion of virus through agar or starch gel, plaque enhancement seems to be the result of the gel becoming positively charged so that viruses can move effectively through them. The observation that starch gel and methylcellulose enhance plaque formation with viruses known to be inhibited under agar was also reinvestigated. When the consistency of the agar gel was reduced to the same viscosity of starch gel and methylcellulose overlays, the same plaque counts and sizes were observed under all three overlays. PMID:4986901

Incorporating Graphene Oxide into Alginate Polymer with a Cationic Intermediate To Strengthen Membrane Dehydration Performance.

PubMed

Guan, Kecheng; Liang, Feng; Zhu, Haipeng; Zhao, Jing; Jin, Wanqin

2018-04-25

Two-dimensional graphene oxide (GO) in hybrid membranes provides fast water transfer across its surface due to the abundant oxygenated functional groups to afford water sorption and the hydrophobic basal plane to create fast transporting pathways. To establish more compatible and efficient interactions for GO and sodium alginate (SA) polymer chains, cations sourced from lignin are employed to decorate GO (labeled as cation-functionalized GO (CG)) nanosheets via cation-π and π-π interactions, providing more interactive sites to confer synergetic benefits with polymer matrix. Cations from CG are also functional to partially interlock SA chains and intensify water diffusion. And with the aid of two-dimensional pathways of CG, fast selective water permeation can be realized through hybrid membranes with CG fillers. In dehydrating aqueous ethanol solution, the hybrid membrane exhibits considerable performance compared with bare SA polymer membrane (long-term stable permeation flux larger than 2500 g m -2 h -1 and water content larger than 99.7 wt %, with feed water content of 10 wt % under 70 °C). The effects of CG content in SA membrane were investigated, and the transport mechanism was correspondingly studied through varying operation conditions and membrane materials. In addition, such a membrane possesses long-term stability and almost unchanged high dehydration capability.

Electrostatic coupling between DNA and its counterions modulates the observed translational diffusion coefficients.

PubMed

Stellwagen, Earle; Stellwagen, Nancy C

2015-09-01

Free solution capillary electrophoresis (CE) is a useful technique for measuring the translational diffusion coefficients of charged analytes. The measurements are relatively fast if the polarity of the electric field is reversed to drive the analyte back and forth past the detection window during each run. We have tested the validity of the resulting diffusion coefficients using double-stranded DNA molecules ranging in size from 20 to 960 base pairs as the model system. The diffusion coefficients of small DNAs are equal to values in the literature measured by other techniques. However, the diffusion coefficients of DNA molecules larger than ∼30 base pairs are anomalously high and deviate increasingly from the literature values with increasing DNA molar mass. The anomalously high diffusion coefficients are due to electrostatic coupling between the DNA and its counterions. As a result, the measured diffusion coefficients vary with the diffusion coefficient of the counterion, as well as with cation concentration and electric field strength. These effects can be reduced or eliminated by measuring apparent diffusion coefficients of the DNA at several different electric field strengths and extrapolating the results to zero electric field.

Two types of diffusions at the cathode/electrolyte interface in IT-SOFCs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li Zhipeng, E-mail: LI.Zhipeng@nims.go.jp; Mori, Toshiyuki; Auchterlonie, Graeme John

2011-09-15

Analytical transmission electron microscopy, in particular with the combination of energy dispersive X-ray spectroscopy (EDX) and electron energy-loss spectroscopy (EELS), has been performed to investigate the microstructure and microchemistry of the interfacial region between the cathode (La{sub 0.6}Sr{sub 0.4}Co{sub 0.8}Fe{sub 0.2}O{sub 3}, LSCF) and the electrolyte (Gd-doped ceria, GDC). Two types of diffusions, mutual diffusion between cathode and electrolyte as well as the diffusion along grain boundaries, have been clarified. These diffusions suggest that the chemical stability of LSCF and GDC are not as good as previously reported. The results are more noteworthy if we take into consideration the factmore » that such interdiffusions occur even during the sintering process of cell preparation. - Graphical Abstract: Two types of diffusions, the mutual diffusion and the diffusion along grain boundaries, occurred at the cathode/electrolyte interface of intermediate temperature solid state fuel cells, during cell preparation. The mutual diffusion is denoted by black arrows and the diffusion along grain boundaries assigned by pink arrows. Highlights: > All the cations in cathode (LSCF) and electrolyte (GDC) can mutually diffuse into each other. > Diffusing elements will segregate at grain boundaries or triple junctions around the cathode/electrolyte interface. > Two types of diffusions, the mutual diffusion and diffusion along grain boundaries, have been clarified thereafter.« less

Nitranilic acid hexahydrate, a novel benchmark system of the Zundel cation in an intrinsically asymmetric environment: spectroscopic features and hydrogen bond dynamics characterised by experimental and theoretical methods.

PubMed

Molčanov, Krešimir; Stare, Jernej; Vener, Mikhail V; Kojić-Prodić, Biserka; Mali, Gregor; Grdadolnik, Jože; Mohaček-Grošev, Vlasta

2014-01-21

Nitranilic acid (2,5-dihydroxy-3,6-dinitro-2,5-cyclohexadiene-1,4-dione) as a strong dibasic acid in acidic aqueous media creates the Zundel cation, H5O2(+). The structural unit in a crystal comprises (H5O2)2(+) (2,5-dihydroxy-3,6-dinitro-1,4-benzoquinonate)(2-) dihydrate where the Zundel cation reveals no symmetry, being an ideal case for studying proton dynamics and its stability. The Zundel cation and proton transfer dynamics are studied by variable-temperature X-ray diffraction, IR and solid-state NMR spectroscopy, and various quantum chemical methods, including periodic DFT calculations, ab initio molecular dynamics simulation, and quantization of nuclear motion along three fully coupled internal coordinates. The Zundel cation features a short H-bond with the O···O distance of 2.433(2) Å with an asymmetric placement of hydrogen. The proton potential is of a single well type and, due to the non-symmetric surroundings, of asymmetric shape. The formation of the Zundel cation is facilitated by the electronegative NO2 groups. The employed spectroscopic techniques supported by calculations confirm the presence of a short H-bond with a complex proton dynamics.

The Steady-State Transport of Oxygen through Hemoglobin Solutions

PubMed Central

Keller, K. H.; Friedlander, S. K.

1966-01-01

The steady-state transport of oxygen through hemoglobin solutions was studied to identify the mechanism of the diffusion augmentation observed at low oxygen tensions. A novel technique employing a platinum-silver oxygen electrode was developed to measure the effective diffusion coefficient of oxygen in steady-state transport. The measurements were made over a wider range of hemoglobin and oxygen concentrations than previously reported. Values of the Brownian motion diffusion coefficient of oxygen in hemoglobin solution were obtained as well as measurements of facilitated transport at low oxygen tensions. Transport rates up to ten times greater than ordinary diffusion rates were found. Predictions of oxygen flux were made assuming that the oxyhemoglobin transport coefficient was equal to the Brownian motion diffusivity which was measured in a separate set of experiments. The close correlation between prediction and experiment indicates that the diffusion of oxyhemoglobin is the mechanism by which steady-state oxygen transport is facilitated. PMID:5943608

Computational study of the RGD-peptide interactions with perovskite-type BFO-(1 1 1) membranes under aqueous conditions

NASA Astrophysics Data System (ADS)

Li, Hai-long; Bian, Liang; Hou, Wen-ping; Dong, Fa-Qin; Song, Mian-Xin; Zhang, Xiao-yan; Wang, Li-sheng

2016-07-01

We elucidated a number of facets regarding arginine-glycine-aspartate (RGD)-bismuth ferrite (BFO)-(1 1 1) membrane interactions and reactivity that have previously remained unexplored on a molecular level. Results demonstrate the intra-molecular interaction facilitates a ;horseshoe; structure of RGD adsorbed onto the BFO-(1 1 1) membrane, through the electrostatic (Asp-cation-Fe) and water-bridge (Osbnd H2O and H2Osbnd NH2) interactions. The effect of structural and electron-transfer interactions is attributed to the cation-valences, indicating that the divalent cations are electron-acceptors and the monovalent cations as electron-donors. Notably, the strongly bound Ca2+ ion exerts a ;gluing; effect on the Asp-side-chain, indicating a tightly packed RGD-BFO configuration. Thus, modulating the biological response of BFO-(1 1 1) membrane will allow us to design more appropriate interfaces for implantable diagnostic and therapeutic perovskite-type micro-devices.

Salting-out and multivalent cation precipitation of anionic surfactants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Walker, R.D. Jr.; Keppel, R.A.; Cosper, M.B.

1981-02-01

In this surfactant/polymer flooding process, a carefully designed surfactant slug is injected into an oil-bearing formation with a view to reducing the oil/water interfacial tension substantially so as to facilitate mobilization of oil droplets trapped in the less accessible void spaces of the reservoir rock. When the surfactant comes into contact with reservoir brine, oil and rock, several phenomena can occur which result in loss of surfactant from the slug, i.e., salting-out of surfactant by NaCl, precipitation of insoluble soaps by multivalent cations such as calcium, partitioning to oil of both dissolved and precipitated surfactant, and adsorption of surfactant onmore » reservoir rock have been identified as important surfactant loss processes. This study presents some experimental data which illustrate the effects of salt and multivalent cations, identifies the mechanisms which are operative, and develops mathematical relationships which enable one to describe the behavior of surfactant systems when brought into contact with salt, multivalent cations, or both. 26 references.« less

Photoenhanced Attachment for Optical Control of Diffuse Discharges.

DTIC Science & Technology

1987-12-31

17 14 . MONTORING AGNC 14AM & OdRSSii I h e en Controlling Office) IS. SECURITY CLASS. (at Chi* report) Unclassified 15m. OECL ASSI F1CATION... 14 References................................................... 15 Publications................................................. 16...substantial translational energy of the fragments. *: This disposition of energy has important consequences in the 14 4 I . * photochemistry and

A new statistical analysis of rare earth element diffusion data in garnet

NASA Astrophysics Data System (ADS)

Chu, X.; Ague, J. J.

2015-12-01

The incorporation of rare earth elements (REE) in garnet, Sm and Lu in particular, links garnet chemical zoning to absolute age determinations. The application of REE-based geochronology depends critically on the diffusion behaviors of the parent and daughter isotopes. Previous experimental studies on REE diffusion in garnet, however, exhibit significant discrepancies that impact interpretations of garnet Sm/Nd and Lu/Hf ages.We present a new statistical framework to analyze diffusion data for REE using an Arrhenius relationship that accounts for oxygen fugacity, cation radius and garnet unit-cell dimensions [1]. Our approach is based on Bayesian statistics and is implemented by the Markov chain Monte Carlo method. A similar approach has been recently applied to model diffusion of divalent cations in garnet [2]. The analysis incorporates recent data [3] in addition to the data compilation in ref. [1]. We also include the inter-run bias that helps reconcile the discrepancies among data sets. This additional term estimates the reproducibility and other experimental variabilities not explicitly incorporated in the Arrhenius relationship [2] (e.g., compositional dependence [3] and water content).The fitted Arrhenius relationships are consistent with the models in ref. [3], as well as refs. [1]&[4] at high temperatures. Down-temperature extrapolation leads to >0.5 order of magnitude faster diffusion coefficients than in refs. [1]&[4] at <750 °C. The predicted diffusion coefficients are significantly slower than ref. [5]. The fast diffusion [5] was supported by a field test of the Pikwitonei Granulite—the garnet Sm/Nd age postdates the metamorphic peak (750 °C) by ~30 Myr [6], suggesting considerable resetting of the Sm/Nd system during cooling. However, the Pikwitonei Granulite is a recently recognized UHT terrane with peak temperature exceeding 900 °C [7]. The revised closure temperature (~730 °C) is consistent with our new diffusion model.[1] Carlson (2012) Am Mineral 97 1598-1618. [2] Chu & Ague (2015) Contrib Mineral Petrol, in press. [3] Bloch et al. (2015) Contrib Mineral Petrol 169 1-18. [4] Van Orman et al. (2002) Contrib Mineral Petrol 142 416-424. [5] Tirone et al. (2005) GCA 69 2385-2398. [6] Mezger et al. (1992) EPSL 113 397-409. [7] Kooijman et al. (2012) J Metamorph Geol 30 397-412.

Increments to chiral recognition facilitating enantiomer separations of chiral acids, bases, and ampholytes using Cinchona-based zwitterion exchanger chiral stationary phases.

PubMed

Wernisch, Stefanie; Pell, Reinhard; Lindner, Wolfgang

2012-07-01

The intramolecular distances of anion and cation exchanger sites of zwitterionic chiral stationary phases represent potential tuning sites for enantiomer selectivity. In this contribution, we investigate the influence of alkanesulfonic acid chain length and flexibility on enantiomer separations of chiral acids, bases, and amphoteric molecules for six Cinchona alkaloid-based chiral stationary phases in comparison with structurally related anion and cation exchangers. Employing polar-organic elution conditions, we observed an intramolecular counterion effect for acidic analytes which led to reduced retention times but did not impair enantiomer selectivities. Retention of amphoteric analytes is based on simultaneous double ion pairing of their charged functional groups with the acidic and basic sites of the zwitterionic selectors. A chiral center in the vicinity of the strong cation exchanger site is vital for chiral separations of bases. Sterically demanding side chains are beneficial for separations of free amino acids. Enantioseparations of free (un-derivatized) peptides were particularly successful in stationary phases with straight-chain alkanesulfonic acid sites, pointing to a beneficial influence of more flexible moieties. In addition, we observed pseudo-enantiomeric behavior of quinine and quinidine-derived chiral stationary phases facilitating reversal of elution orders for all analytes. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A Two-Phase Intergrowth in Genthelvite from Mont Saint-Hilaire, Quebec

DOE Office of Scientific and Technical Information (OSTI.GOV)

Antao, Sytle M.; Hassan, Ishmael; West Indies)

Synchrotron high-resolution powder X-ray-diffraction (HRPXRD) data and Rietveld structure refinement were used to examine a two-phase intergrowth of genthelvite, ideally Zn{sub 8}[Be{sub 6}Si{sub 6}O{sub 24}]S{sub 2}, from the alkaline intrusive complex at Mont Saint-Hilaire, Quebec, where genthelvite occurs in nepheline syenite pegmatites. The structural parameters obtained for the two phases are slightly different from each other. The unit-cell parameters are 8.119190(7) {angstrom} (51% phase 1) and 8.128914(9) {angstrom} (49% phase 2). The refinement gives the chemical formulae and interstitial M cation in terms of Zn and Mn (the Fe content is practically zero) for the Mn-poor genthelvite phase 1 asmore » (Zn{sub 7.8}Mn{sub 0.2}){Sigma}{sub 8}[Be{sub 6}Si{sub 6}O{sub 24}]S{sub 2}, and the Mn-rich genthelvite phase 2 as (Zn{sub 7.0}Mn{sub 1.0}){Sigma}{sub 8}[Be{sub 6}Si{sub 6}O{sub 24}]S{sub 2}. These formulae are comparable to the Mn-poor and Mn-rich phases obtained by electron-microprobe analysis. The intergrowth indicates that diffusion is absent among the interstitial M cations of similar size (Zn{sup 2+}, Fe{sup 2+} and Mn{sup 2+}). Such intergrowths may form under distinct f(O{sub 2}) conditions and probably low temperature of crystallization that inhibits diffusion of M cations.« less

Anion exchange membranes composed of a poly(2,6-dimethyl-1,4-phenylene oxide) random copolymer functionalized with a bulky phosphonium cation

DOE PAGES

Liu, Ye; Zhang, Bingzi; Kinsinger, Corey L.; ...

2016-01-22

A random copolymer, tris(2,4,6-trimethoxyphenyl) phosphonium functionalized poly(2,6-dimethyl-1,4-phenylene oxide) (PPO-TPQP) was cast from three different solvents: dimethyl sulfoxide (DMSO), ethyl lactate, or a 41:59 vol% mixture of DMSO and ethyl lactate. Solvents were selected via analysis of the Hansen solubility parameters to vary the phase separation of the polymer in the films. An optimized mixture of DMSO and ethyl lactate chosen for film fabrication and this film was contrasted with films cast from the neat constituent solvents. Atomic force microscopy identified domains from nanometer to tens of nanometer sizes, while the light microscopy showed features on the order of micron. SAXSmore » revealed a cation scattering peak with a d-spacing from 7 to 15 Å. Trends in conductivity and water diffusion for the membranes vary depending on the solvent from which they are cast. The mixed solvent cast membrane shows a linear Arrhenius behavior indicating fully dissociated cationic/anionic groups, and has the highest bromide conductivity of 3 mS/cm at 95% RH, 90 °C. The ethyl lactate cast membrane shows a linear Arrhenius relation in conductivity, but a Vogel-Tamman-Fulcher behavior in its water self-diffusion. While water increases bromide dissociation, water and bromide transport in these films seems to be decoupled. Lastly, this is particularly true for the film cast from ethyl lactate.« less

Anion exchange membranes composed of a poly(2,6-dimethyl-1,4-phenylene oxide) random copolymer functionalized with a bulky phosphonium cation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Ye; Zhang, Bingzi; Kinsinger, Corey L.

A random copolymer, tris(2,4,6-trimethoxyphenyl) phosphonium functionalized poly(2,6-dimethyl-1,4-phenylene oxide) (PPO-TPQP) was cast from three different solvents: dimethyl sulfoxide (DMSO), ethyl lactate, or a 41:59 vol% mixture of DMSO and ethyl lactate. Solvents were selected via analysis of the Hansen solubility parameters to vary the phase separation of the polymer in the films. An optimized mixture of DMSO and ethyl lactate chosen for film fabrication and this film was contrasted with films cast from the neat constituent solvents. Atomic force microscopy identified domains from nanometer to tens of nanometer sizes, while the light microscopy showed features on the order of micron. SAXSmore » revealed a cation scattering peak with a d-spacing from 7 to 15 A. Trends in conductivity and water diffusion for the membranes vary depending on the solvent from which they are cast. The mixed solvent cast membrane shows a linear Arrhenius behavior indicating fully dissociated cationic/anionic groups, and has the highest bromide conductivity of 3 mS/cm at 95% RH, 90 degrees C. The ethyl lactate cast membrane shows a linear Arrhenius relation in conductivity, but a Vogel-Tamman-Fulcher behavior in its water self-diffusion. While water increases bromide dissociation, water and bromide transport in these films seems to be decoupled. This is particularly true for the film cast from ethyl lactate.« less

Anion exchange membranes composed of a poly(2,6-dimethyl-1,4-phenylene oxide) random copolymer functionalized with a bulky phosphonium cation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Ye; Zhang, Bingzi; Kinsinger, Corey L.

A random copolymer, tris(2,4,6-trimethoxyphenyl) phosphonium functionalized poly(2,6-dimethyl-1,4-phenylene oxide) (PPO-TPQP) was cast from three different solvents: dimethyl sulfoxide (DMSO), ethyl lactate, or a 41:59 vol% mixture of DMSO and ethyl lactate. Solvents were selected via analysis of the Hansen solubility parameters to vary the phase separation of the polymer in the films. An optimized mixture of DMSO and ethyl lactate chosen for film fabrication and this film was contrasted with films cast from the neat constituent solvents. Atomic force microscopy identified domains from nanometer to tens of nanometer sizes, while the light microscopy showed features on the order of micron. SAXSmore » revealed a cation scattering peak with a d-spacing from 7 to 15 Å. Trends in conductivity and water diffusion for the membranes vary depending on the solvent from which they are cast. The mixed solvent cast membrane shows a linear Arrhenius behavior indicating fully dissociated cationic/anionic groups, and has the highest bromide conductivity of 3 mS/cm at 95% RH, 90 °C. The ethyl lactate cast membrane shows a linear Arrhenius relation in conductivity, but a Vogel-Tamman-Fulcher behavior in its water self-diffusion. While water increases bromide dissociation, water and bromide transport in these films seems to be decoupled. Lastly, this is particularly true for the film cast from ethyl lactate.« less

Quantitative characterization of non-classic polarization of cations on clay aggregate stability.

PubMed

Hu, Feinan; Li, Hang; Liu, Xinmin; Li, Song; Ding, Wuquan; Xu, Chenyang; Li, Yue; Zhu, Longhui

2015-01-01

Soil particle interactions are strongly influenced by the concentration, valence and ion species and the pH of the bulk solution, which will also affect aggregate stability and particle transport. In this study, we investigated clay aggregate stability in the presence of different alkali ions (Li+, Na+, K+, and Cs+) at concentrations from10-5 to 10-1 mol L-1. Strong specific ion effects on clay aggregate stability were observed, and showed the order Cs+>K+>Na+>Li+. We found that it was not the effects of ion size, hydration, and dispersion forces in the cation-surface interactions but strong non-classic polarization of adsorbed cations that resulted in these specific effects. In this study, the non-classic dipole moments of each cation species resulting from the non-classic polarization were estimated. By comparing non-classic dipole moments with classic values, the observed dipole moments of adsorbed cations were up to 104 times larger than the classic values for the same cation. The observed non-classic dipole moments sharply increased with decreasing electrolyte concentration. We conclude that strong non-classic polarization could significantly suppress the thickness of the diffuse layer, thereby weakening the electric field near the clay surface and resulting in improved clay aggregate stability. Even though we only demonstrated specific ion effects on aggregate stability with several alkali ions, our results indicate that these effects could be universally important in soil aggregate stability.

Correlation of transarterial transport of various dextrans with their physicochemical properties.

PubMed

Elmalak, O; Lovich, M A; Edelman, E

2000-11-01

Local vascular drug delivery provides elevated concentrations of drug in the target tissue while minimizing systemic side effects. To better characterize local pharmacokinetics we examined the arterial transport of locally applied dextran and dextran derivatives in vivo. Using a two-compartment pharmacokinetic model to correct the measured transmural flux of these compounds for systemic redistribution and elimination as delivered from a photopolymerizable hydrogel surrounding rat carotid arteries, we found that the diffusivities and the transendothelial permeabilities were strongly dependent on molecular weight and charge. For neutral dextrans, the effective diffusive resistance in the media increased with molecular weight approximately 4.1-fold between the molecular weights of 10 and 282 kDa. Similarly, endothelial resistance increased 28-fold over the same molecular weight range. The effective medial diffusive resistance was unaffected by cationic charge as such molecules moved identically to neutral compounds, but increased approximately 40% when dextrans were negatively charged. Transendothelial resistance was 20-fold lower for the cationic dextrans, and 11-fold higher for the anionic dextrans, when both were compared to neutral counterparts. These results suggest that, while low molecular weight drugs will rapidly traverse the arterial wall with the endothelium posing a minimal barrier, the reverse is true for high molecular weight agents. With these data, the deposition and distribution of locally released vasotherapeutic compounds might be predicted based upon chemical properties, such as molecular weight and charge.

Theory of the formation of the electric double layer at the ion exchange membrane-solution interface.

PubMed

Moya, A A

2015-02-21

This work aims to extend the study of the formation of the electric double layer at the interface defined by a solution and an ion-exchange membrane on the basis of the Nernst-Planck and Poisson equations, including different values of the counter-ion diffusion coefficient and the dielectric constant in the solution and membrane phases. The network simulation method is used to obtain the time evolution of the electric potential, the displacement electric vector, the electric charge density and the ionic concentrations at the interface between a binary electrolyte solution and a cation-exchange membrane with total co-ion exclusion. The numerical results for the temporal evolution of the interfacial electric potential and the surface electric charge are compared with analytical solutions derived in the limit of the shortest times by considering the Poisson equation for a simple cationic diffusion process. The steady-state results are justified from the Gouy-Chapman theory for the diffuse double layer in the limits of similar and high bathing ionic concentrations with respect to the fixed-charge concentration inside the membrane. Interesting new physical insights arise from the interpretation of the process of the formation of the electric double layer at the ion exchange membrane-solution interface on the basis of a membrane model with total co-ion exclusion.

Diffusion and Electric Mobility of Ions within Isolated Cuticles of Citrus aurantium 1

PubMed Central

Tyree, Melvin T.; Wescott, Charles R.; Tabor, Christopher A.

1991-01-01

We report a new method for measuring cation and anion permeability across cuticles of sour orange, Citrus aurantium, leaves. The method requires the measurement of two electrical parameters: the diffusion potential arising when the two sides of the cuticle are bathed in unequal concentrations of a Cl− salt; and the electrical conductance of the cuticle measured at a salt concentration equal to the average of that used in the diffusion-potential measurement. The permeabilities of H+, Li+, Na+, K+, and Cs+ ranged from 2 × 10−8 to 0.6 × 10−8 meters per second when cuticles were bathed in 2 moles per cubic meter Cl− salts. The permeability of Cl− was 3 × 10−9 meters per second. The permeability of Li+, Na+, and K+ was about five times less when measured in 500 moles per cubic meter Cl− salts. We also report an asymmetry in cuticle-conductance values depending on the magnitude and the direction of current flow. The asymmetry disappears at low current-pulse magnitude and increases linearly with the magnitude of the current pulse. This phenomenon is explained in terms of transport-number effects in a bilayer model of the cuticle. Conductance is not augmented by current carried by exchangeable cations in cuticles; conductance is rate limited by the outer waxy layer of the cuticle. PMID:16668382

Understanding the anisotropic strain effects on lithium diffusion in graphite anodes: A first-principles study

NASA Astrophysics Data System (ADS)

Ji, Xiang; Wang, Yang; Zhang, Junqian

2018-06-01

The lithium diffusion in graphite anode, which is the most widely used commercial electrode material today, affects the charge/discharge performance of lithium-ion batteries. In this study, the anisotropic strain effects on lithium diffusion in graphite anodes are systematically investigated using first-principles calculations based on density functional theory (DFT) with van der Waals corrections. It is found that the effects of external applied strains along various directions of LixC6 (i.e., perpendicular or parallel to the basal planes of the graphite host) on lithium diffusivity are different. Along the direction perpendicular to the graphite planes, the tensile strain facilitates in-plane Li diffusion by reducing the energy barrier, and the compressive strain hinders in-plane Li diffusion by raising the energy barrier. In contrast, the in-plane biaxial tensile strain (parallel to the graphite planes) hinders in-plane Li diffusion, and the in-plane biaxial compressive strain facilitates in-plane Li diffusion. Furthermore, both in-plane and transverse shear strains slightly influence Li diffusion in graphite anodes. A discussion is presented to explain the anisotropic strain dependence of lithium diffusion. This research provides data for the continuum modelling of the electrodes in the lithium-ion batteries.

Effects of Zinc Gluconate and 2 Other Divalent Cationic Compounds on Olfactory Function in Mice

PubMed Central

Duncan-Lewis, Christopher A; Lukman, Roy L; Banks, Robert K

2011-01-01

Intranasal application of zinc gluconate has commonly been used to treat the common cold. The safety of this treatment, however, has come into question recently. In addition to a United States recall of a homeopathic product that contains zinc gluconate, abundant literature reports cytotoxic effects of zinc on the olfactory epithelium. Additional research suggests that divalent cations (such as zinc) can block ion channels that facilitate the transduction of odors into electrical signals on the olfactory epithelium. The purpose of the current study was 2-fold: to confirm whether zinc gluconate causes anosmia and to reveal whether any other divalent cationic compounds produce a similar effect. Groups of mice underwent a buried food-pellet test to gauge olfactory function and then were nasally irrigated with 1 of 3 divalent cationic compounds. When tested after treatment, mice irrigated with zinc gluconate and copper gluconate experienced a marked increase in food-finding time, indicating that they had lost their ability to smell a hidden food source. Control mice irrigated with saline had a significantly lower increase in times. These results confirm that zinc gluconate can cause anosmia and reveal that multiple divalent cations can negatively affect olfaction. PMID:22330252

Polymerization Initiated at the Sidewalls of Carbon Nanotubes

NASA Technical Reports Server (NTRS)

Tour, James M.; Hudson, Jared L.

2011-01-01

A process has been developed for growing polymer chains via anionic, cationic, or radical polymerization from the side walls of functionalized carbon nanotubes, which will facilitate greater dispersion in polymer matrices, and will greatly enhance reinforcement ability in polymeric material.

Investigation of Oxygen Diffusion in Irradiated UO2 with MD Simulation

NASA Astrophysics Data System (ADS)

Günay, Seçkin D.

2016-11-01

In this study, irradiated UO2 is analyzed by atomistic simulation method to obtain diffusion coefficient of oxygen ions. For this purpose, a couple of molecular dynamics (MD) supercells containing Frenkel, Schottky, vacancy and interstitial types for both anion and cation defects is constructed individually. Each of their contribution is used to calculate the total oxygen diffusion for both intrinsic and extrinsic ranges. The results display that irradiation-induced defects contribute the most to the overall oxygen diffusion at temperatures below 800-1,200 K. This result is quite sensible because experimental data shows that, from room temperature to about 1,500 K, irradiation-induced swelling decreases and irradiated UO2 lattice parameter is gradually recovered because defects annihilate each other. Another point is that, concentration of defects enhances the irradiation-induced oxygen diffusion. Irradiation type also has the similar effect, namely oxygen diffusion in crystals irradiated with α-particles is more than the crystals irradiated with neutrons. Dynamic Frenkel defects dominate the oxygen diffusion data above 1,500—1,800 K. In all these temperature ranges, thermally induced Frenkel defects make no significant contribution to overall oxygen diffusion.

NMR Water Self–Diffusion and Relaxation Studies on Sodium Polyacrylate Solutions and Gels in Physiologic Ionic Solutions

PubMed Central

Bai, Ruiliang; Basser, Peter J.; Briber, Robert M.; Horkay, Ferenc

2013-01-01

Water self-diffusion coefficients and longitudinal relaxation rates in sodium polyacrylate solutions and gels were measured by NMR, as a function of polymer content and structure in a physiological concentration range of monovalent and divalent cations, Ca2+ and Na+. Several physical models describing the self-diffusion of the solvent were applied and compared. A free-volume model was found to be in good agreement with the experimental results over a wide range of polymer concentrations. The longitudinal relaxation rate exhibited linear dependence on polymer concentration below a critical concentration and showed non-linear behavior at higher concentrations. Both the water self-diffusion and relaxation were less influenced by the polymer in the gel state than in the uncrosslinked polymer solutions. The effect of Na+ on the mobility of water molecules was practically undetectable. By contrast, addition of Ca2+ strongly increased the longitudinal relaxation rate while its effect on the self-diffusion coefficient was much less pronounced. PMID:24409001

NMR Water Self-Diffusion and Relaxation Studies on Sodium Polyacrylate Solutions and Gels in Physiologic Ionic Solutions.

PubMed

Bai, Ruiliang; Basser, Peter J; Briber, Robert M; Horkay, Ferenc

2014-03-15

Water self-diffusion coefficients and longitudinal relaxation rates in sodium polyacrylate solutions and gels were measured by NMR, as a function of polymer content and structure in a physiological concentration range of monovalent and divalent cations, Ca 2+ and Na + . Several physical models describing the self-diffusion of the solvent were applied and compared. A free-volume model was found to be in good agreement with the experimental results over a wide range of polymer concentrations. The longitudinal relaxation rate exhibited linear dependence on polymer concentration below a critical concentration and showed non-linear behavior at higher concentrations. Both the water self-diffusion and relaxation were less influenced by the polymer in the gel state than in the uncrosslinked polymer solutions. The effect of Na + on the mobility of water molecules was practically undetectable. By contrast, addition of Ca 2+ strongly increased the longitudinal relaxation rate while its effect on the self-diffusion coefficient was much less pronounced.

On the role of humic acids' carboxyl groups in the binding of charged organic compounds.

PubMed

Smilek, Jiří; Sedláček, Petr; Kalina, Michal; Klučáková, Martina

2015-11-01

Interactions of humic acids (HAs) with two cationic dyes (methylene blue and rhodamine 6G) were studied using a unique combination of diffusion and partitioning studies in HAs, containing hydrogels and batch sorption experiments. In order to investigate the involvement of carboxyl groups of HAs in these interactions, all experiments were performed for both, the original lignite HAs and HAs with selectively methylated carboxyls. The results of the diffusion experiments confirm that the interactions between the solute and humic substances have a strong impact on the rate of diffusion process. Surprisingly, the effect is almost equally approved for original and methylated HAs. On the other hand, the results of batch sorption experiments show strong improvement of the sorption capacity (methylated HAs), which is explained by changed morphology of alkylated HAs. The comparison of the results of diffusion and adsorption experiments shows that the diffusion experiments simulate the transport of solutes in natural humics containing environment more reasonably. Copyright © 2015 Elsevier Ltd. All rights reserved.

Modeling transport kinetics in clinoptilolite-phosphate rock systems

NASA Technical Reports Server (NTRS)

Allen, E. R.; Ming, D. W.; Hossner, L. R.; Henninger, D. L.

1995-01-01

Nutrient release in clinoptilolite-phosphate rock (Cp-PR) systems occurs through dissolution and cation-exchange reactions. Investigating the kinetics of these reactions expands our understanding of nutrient release processes. Research was conducted to model transport kinetics of nutrient release in Cp-PR systems. The objectives were to identify empirical models that best describe NH4, K, and P release and define diffusion-controlling processes. Materials included a Texas clinoptilolite (Cp) and North Carolina phosphate rock (PR). A continuous-flow thin-disk technique was used. Models evaluated included zero order, first order, second order, parabolic diffusion, simplified Elovich, Elovich, and power function. The power-function, Elovich, and parabolic-diffusion models adequately described NH4, K, and P release. The power-function model was preferred because of its simplicity. Models indicated nutrient release was diffusion controlled. Primary transport processes controlling nutrient release for the time span observed were probably the result of a combination of several interacting transport mechanisms.

Kinetic model for the short-term dissolution of a rhyolitic glass

USGS Publications Warehouse

White, A.F.; Claassen, H.C.

1980-01-01

Aqueous dissolution experiments with the vitric phase of a rhyolitic tuff were performed at 25??C and constant pH in the range 4.5-7.5. Results suggest interchange of aqueous hydrogen ions for cations situated both on the surface and within the glass. At time intervals from 24 to 900 hr., dissolution kinetics are controlled by ion transport to and from sites within the glass. Experimental data indicate that parabolic diffusion rate of a chemical species from the solid is a nonlinear function of its aqueous concentration. A numerical solution to Fick's second law is presented for diffusion of sodium, which relates it's aqueous concentration to it's concentration on glass surface, by a Freundlich adsorption isotherm. The pH influence on sodium diffusion in the model can be accounted for by use of a pH-dependent diffusion coefficient and a pH-independent adsorption isotherm. ?? 1980.

Mid and Near-IR Absorption Spectra of PAH Neutrals and Ions in H20 Ice to Facilitate their Astronomical Detection

NASA Technical Reports Server (NTRS)

Bernstein, Max P.; Sandford, Scott A.; Allamandola, Louis J.

2004-01-01

Polycyclic aromatic hydrocarbons (PAHs) are believed to be the most abundant and widespread class of organic compounds in the universe, having been observed in emission towards energetic regions and absorption towards colder ones.We will present IR spectra of PAHs and their cations in H20 ice measured in the laboratory in the hopes that this will facilitate the detection of these features in the interstellar medium.

Transports of ionic liquids in ionic polymer conductor network composite actuators

NASA Astrophysics Data System (ADS)

Liu, Yang; Liu, Sheng; Lin, Junhong; Wang, Dong; Jain, Vaibhav; Montazami, Reza; Heflin, James R.; Li, Jing; Madsen, Louis; Zhang, Q. M.

2010-04-01

We investigate the influence of ionic liquids on the electromechanical performance of Ionic Polymer Conductor Network Composite (IPCNC) bending actuators. Two imidazolium ionic liquids (ILs) with one cation, which is 1-ethyl-3- methylimidazolium ([EMI+]), and two different anions, which are tetrafluoroborate ([BF4-]) and trifluoromethanesulfonate ([Tf-]), are chosen for the study. By combining the time domain electric and electromechanical responses, we developed a new model that describes the ion transports in IPCNC actuators. The time constant of excess cation and anion migration in various composite electrodes are deduced: 6s and 25s in RuO2/Nafion; 7.9s and 36.3s in RuO2/Aquivion; 4.8s and 53s in Au/PAH, respectively. NMR is also applied to provide quantitative measures of self-diffusion coefficients independently for IL anions and cations both in pure ILs and in ILs absorved into ionomers. All the results indicate that the motion of cation, in the studied pure ionic liquids, polymer matrix and conductor network composites, is faster than that of anion. Moreover, the CNC morphology is playing a crucial role in determining the ion transport in the porous electrodes.

Transport of Organic Compounds Through Porous Systems Containing Humic Acids.

PubMed

Smilek, Jiri; Sedlacek, Petr; Lastuvkova, Marcela; Kalina, Michal; Klucakova, Martina

2017-03-01

Soil pollution by the presence of different contaminants (e.g. heavy metal ions or pesticides) is one of the biggest problems worldwide. The positive affinity of natural humic acids towards these contaminants might contribute to the soil and ground water protection; therefore it is necessary to study the reactivity and barrier properties of humic acids. An original reactivity-mapping tool based on diffusion techniques designed to study the reactivity and barrier properties of polyelectrolytes was developed and tested on humic acids. The results of diffusion experiments demonstrate that the electrostatic interactions between humic acids functioning as a polyelectrolyte interpenetrated in a supporting hydrogel matrix (agarose) and cationic dye (methylene blue) as a model solute have a crucial impact on the rate of diffusion processes and on the barrier properties of hydrogels. The intensity of interactions was evaluated by fundamental diffusion parameters (effective diffusion coefficients and breakthrough time). The impact of modification of humic acids was also studied by means of diffusion experiments conducted on two types of standard humic acids (Leonardite 1S104H) and humic acids with selectively methylated carboxylic groups.

Modeling of bleach plant washer mineral scale

Treesearch

Alan Rudie; Peter Hart

2004-01-01

One of the more common areas of mineral scale formation in bleach plants is on washer face wires and the extraction rings of diffusion washers. Whereas most scale problems can be understood as a mixing of two streams that increase the concentrations of anions and cations and exceed a solubility product, washer problems are often more difficult to understand. The...

Solid Solutions of Rare Earth Cations in Mesoporous Anatase Beads and Their Performances in Dye-Sensitized Solar Cells

PubMed Central

Cavallo, Carmen; Salleo, Alberto; Gozzi, Daniele; Di Pascasio, Francesco; Quaranta, Simone; Panetta, Riccardo; Latini, Alessandro

2015-01-01

Solid solutions of the rare earth (RE) cations Pr3+, Nd3+, Sm3+, Gd3+, Er3+ and Yb3+ in anatase TiO2 have been synthesized as mesoporous beads in the concentration range 0.1–0.3% of metal atoms. The solid solutions were have been characterized by XRD, SEM, diffuse reflectance UV-Vis spectroscopy, BET and BJH surface analysis. All the solid solutions possess high specific surface areas, up to more than 100 m2/g. The amount of adsorbed dye in each photoanode has been determined spectrophotometrically. All the samples were tested as photoanodes in dye-sensitized solar cells (DSSCs) using N719 as dye and a nonvolatile, benzonitrile based electrolyte. All the cells were have been tested by conversion efficiency (J–V), quantum efficiency (IPCE), electrochemical impedance spectroscopy (EIS) and dark current measurements. While lighter RE cations (Pr3+, Nd3+) limit the performance of DSSCs compared to pure anatase mesoporous beads, cations from Sm3+ onwards enhance the performance of the devices. A maximum conversion efficiency of 8.7% for Er3+ at a concentration of 0.2% has been achieved. This is a remarkable efficiency value for a DSSC employing N719 dye without co-adsorbents and a nonvolatile electrolyte. For each RE cation the maximum performances are obtained for a concentration of 0.2% metal atoms. PMID:26577287

Electrospray ionization tandem mass spectrometry of ammonium cationized polyethers.

PubMed

Nasioudis, Andreas; Heeren, Ron M A; van Doormalen, Irene; de Wijs-Rot, Nicolette; van den Brink, Oscar F

2011-05-01

Quaternary ammonium salts (Quats) and amines are known to facilitate the MS analysis of high molar mass polyethers by forming low charge state adduct ions. The formation, stability, and behavior upon collision-induced dissociation (CID) of adduct ions of polyethers with a variety of Quats and amines were studied by electrospray ionization quadrupole time-of-flight, quadrupole ion trap, and linear ion trap tandem mass spectrometry (MS/MS). The linear ion trap instrument was part of an Orbitrap hybrid mass spectrometer that allowed accurate mass MS/MS measurements. The Quats and amines studied were of different degree of substitution, structure, and size. The stability of the adduct ions was related to the structure of the cation, especially the amine's degree of substitution. CID of singly/doubly charged primary and tertiary ammonium cationized polymers resulted in the neutral loss of the amine followed by fragmentation of the protonated product ions. The latter reveals information about the monomer unit, polymer sequence, and endgroup structure. In addition, the detection of product ions retaining the ammonium ion was observed. The predominant process in the CID of singly charged quaternary ammonium cationized polymers was cation detachment, whereas their doubly charged adduct ions provided the same information as the primary and tertiary ammonium cationized adduct ions. This study shows the potential of specific amines as tools for the structural elucidation of high molar mass polyethers. © American Society for Mass Spectrometry, 2011

RISE-306; State Facilitator Program Evaluation, 1975-1976.

ERIC Educational Resources Information Center

Communication Technology Corp., Marlton, NJ.

As an arm of the National Diffusion Network, the Pennsylvania State Facilitator's responsibilities include informing the schools about Title III approved programs and aiding in the actual adoption of such programs by school districts. Two aspects of the facilitator's role were identified for evaluation: (1) whether the facilitator had implemented…

Combined Hydrous Ferric Oxide and Quaternary Ammonium Surfactant Tailoring of Granular Activated Carbon for Concurrent Arsenate and Perchlorate Removal

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jang, M.; Cannon, F; Parette, R

2009-01-01

Activated carbon was tailored with both iron and quaternary ammonium surfactants so as to concurrently remove both arsenate and perchlorate from groundwater. The iron (hydr)oxide preferentially removed the arsenate oxyanion but not perchlorate; while the quaternary ammonium preferentially removed the perchlorate oxyanion, but not the arsenate. The co-sorption of two anionic oxyanions via distinct mechanisms has yielded intriguing phenomena. Rapid small-scale column tests (RSSCTs) with these dually prepared media employed synthetic waters that were concurrently spiked with arsenate and perchlorate; and these trial results showed that the quaternary ammonium surfactants enhanced arsenate removal bed life by 25-50% when compared tomore » activated carbon media that had been preloaded merely with iron (hydr)oxide; and the surfactant also enhanced the diffusion rate of arsenate per the Donnan effect. The authors also employed natural groundwater from Rutland, MA which contained 60 microg/L As and traces of silica, and sulfate; and the authors spiked this with 40 microg/L perchlorate. When processing this water, activated carbon that had been tailored with iron and cationic surfactant could treat 12,500 bed volumes before 10 microg/L arsenic breakthrough, and 4500 bed volumes before 6 microg/L perchlorate breakthrough. Although the quaternary ammonium surfactants exhibited only a slight capacity for removing arsenate, these surfactants did facilitate a more favorably positively charged avenue for the arsenate to diffuse through the media to the iron sorption site (i.e. via the Donnan effect).« less

Fundamentally Addressing Bromine Storage through Reversible Solid-State Confinement in Porous Carbon Electrodes: Design of a High-Performance Dual-Redox Electrochemical Capacitor.

PubMed

Yoo, Seung Joon; Evanko, Brian; Wang, Xingfeng; Romelczyk, Monica; Taylor, Aidan; Ji, Xiulei; Boettcher, Shannon W; Stucky, Galen D

2017-07-26

Research in electric double-layer capacitors (EDLCs) and rechargeable batteries is converging to target systems that have battery-level energy density and capacitor-level cycling stability and power density. This research direction has been facilitated by the use of redox-active electrolytes that add faradaic charge storage to increase energy density of the EDLCs. Aqueous redox-enhanced electrochemical capacitors (redox ECs) have, however, performed poorly due to cross-diffusion of soluble redox couples, reduced cycle life, and low operating voltages. In this manuscript, we propose that these challenges can be simultaneously met by mechanistically designing a liquid-to-solid phase transition of oxidized catholyte (or reduced anolyte) with confinement in the pores of electrodes. Here we demonstrate the realization of this approach with the use of bromide catholyte and tetrabutylammonium cation that induces reversible solid-state complexation of Br 2 /Br 3 - . This mechanism solves the inherent cross-diffusion issue of redox ECs and has the added benefit of greatly stabilizing the reactive bromine generated during charging. Based on this new mechanistic insight on the utilization of solid-state bromine storage in redox ECs, we developed a dual-redox EC consisting of a bromide catholyte and an ethyl viologen anolyte with the addition of tetrabutylammonium bromide. In comparison to aqueous and organic electric double-layer capacitors, this system enhances energy by factors of ca. 11 and 3.5, respectively, with a specific energy of ∼64 W·h/kg at 1 A/g, a maximum power density >3 kW/kg, and cycling stability over 7000 cycles.

Application of SR Methods for the Study of Nanocomposite Materials for Hydrogen Energy

NASA Astrophysics Data System (ADS)

Sadykov, V. A.; Pavlova, S. N.; Vinokurov, Z. S.; Shmakov, A. N.; Eremeev, N. F.; Fedorova, Yu. E.; Yakimchuk, E. P.; Kriventsov, V. V.; Bolotov, V. A.; Tanashev, Yu. Yu.; Sadovskaya, E. M.; Cherepanova, S. V.; Zolotarev, K. V.

This work summarizes results of synchrotron radiation (SR) studies of the real/defect structure of nanocrystalline/nanocomposite oxide materials, which determines their functional properties in hydrogen energy field as catalysts and mixed ionic electronic conductors (cathodes and anodes of solid oxide fuel cells, oxygen separation membranes). For nanocrystalline ceria-zirconia mixed oxide prepared via modified Pechini route using ethanol solution of reagents, a high spatial uniformity of cations distribution between domains along with the oxygen sublattice deficiency revealed by full-profile Rietveld refinement of SR diffraction data provide structure disordering enhancing oxygen mobility. For PrNi0.5Co0.5O3-δ - Ce0.9Y0.1O2-δ nanocomposite extensive transfer of Pr cations into fluorite domains generates a new path of fast oxygen diffusion along chains of Pr3+ - Pr4+ cations as directly proved by analysis of the unit cell relaxation after changing pO2 in perfect agreement with data obtained by oxygen isotope heteroexchange.

Synthesis and characterization of heterometallic uranyl pyridinedicarboxylate compounds

NASA Astrophysics Data System (ADS)

Jayasinghe, Ashini S.; Payne, Maurice K.; Forbes, Tori Z.

2017-10-01

The incorporation of transition metals into hybrid uranyl materials can result in more diverse structural topologies and variations in physical and chemical properties. To explore the impact of transition metals on the uranyl cation, five uranium containing bimetallic chain compounds, [(UO2)M(PDC)2(H2O)4]·4(H2O) (PDC = 2,6 pyridinedicarboxylate; M = Ni2+, Co2+, Fe2+, Zn2+, and Cu2+) were synthesized by evaporation of aqueous solutions at room temperature. The uranyl cation is complex by two PDC ligands and the transition metal cations bond to the complex to form a one-dimensional chain topology. The presence of the transition metal leads to the presence of a stronger uranyl oxo bonds as shown by the single-crystal X-ray diffraction data and the Raman spectra. Solid state diffuse reflectance UV/Visible spectra confirmed the presence of the transition metals in the structure by the broad bands that appeared at relevant wavelengths.

Functional selectivity of GPCR-directed drug action through location bias

PubMed Central

Irannejad, Roshanak; Pessino, Veronica; Mika, Delphine; Huang, Bo; Wedegaertner, Philip B.; Conti, Marco; von Zastrow, Mark

2017-01-01

G protein-coupled receptors (GPCRs) are increasingly recognized to operate from intracellular membranes as well as the plasma membrane. The β2-adrenergic GPCR can activate Gs-linkedcyclic AMP (cAMP) signaling from endosomes. We show here that the homologous human β1-adrenergic receptor initiates an internal Gs-cAMP signal from the Golgi apparatus. By developing a chemical method to acutely squelch G protein coupling at defined membrane locations, we demonstrate that Golgi activation contributes significantly to the overall cellular cAMP response. Golgi signalling utilizes a pre-existing receptor pool rather than receptors delivered from the cell surface, requiring separate access of extracellular ligands. Epinephrine, a hydrophilic endogenous ligand, accesses the Golgi-localized receptor pool by facilitated transport requiring the organic cation transporter 3 (OCT3) whereas drugs can access the Golgi pool by passive diffusion according to hydrophobicity. We demonstrate marked differences among both agonist and antagonist drugs in Golgi-localized receptor access, and show that β-blocker drugs presently used in the clinic differ markedly in ability to antagonize the Golgi signal. We propose ’location bias’ as a new principle for achieving functional selectivity of GPCR-directed drug action. PMID:28553949

Characterization of the ZAT1p zinc transporter from Arabidopsis thaliana in microbial model organisms and reconstituted proteoliposomes.

PubMed

Bloss, Tanja; Clemens, Stephan; Nies, Dietrich H

2002-03-01

The ZAT1p zinc transporter from Arabidopsis thaliana (L.) Heynh. is a member of the cation diffusion facilitator (CDF) protein family. When heterologously expressed in Escherichia coli, ZAT1p bound zinc in a metal blot. Binding of zinc occurred mainly to the hydrophilic amino acid region from H182 to H232. A ZAT1p/ZAT1p*Delta(M1-I25) protein mixture was purified and reconstituted into proteoliposomes. Uptake of zinc into the proteoliposomes did not require a proton gradient across the liposomal membrane. ZAT1p did not transport cobalt, and transported cadmium at only 1% of the zinc transport rate. ZAT1p functioned as an uptake system for 65Zn2+ in two strains of the Gram-negative bacterium Ralstonia metallidurans, which were different in their content of zinc-efflux systems. The ZAT1 gene did not rescue increased zinc sensitivity of a Delta ZRC1single-mutant strain or of a Delta ZRC1 Delta COT1 double-mutant strain of Saccharomyces cerevisiae, but ZAT1 complemented this phenotype in a Delta SpZRC1 mutant strain of Schizosaccharomyces pombe.

Hydrogen depassivation of the magnesium acceptor by beryllium in p-type GaN

NASA Astrophysics Data System (ADS)

Wang, Chihsiang; Wang, Xiao; Zhang, Qiming

2010-05-01

Under nitrogen-rich growth conditions, the present ab initio study predicts that hydrogen passivation is more effective on the acceptor Be instead of Mg in a co-doped p-type GaN. The formation energy is 0.24 eV for (H-Be Ga) complex, and 0.46 eV for (H-Mg Ga) complex. Congruently, the binding energy is 1.40 eV for (H-Be Ga), and 0.60 eV for (H-Mg Ga). Owing to the lower binding energy, (H-Mg Ga) is not thermally stable. As Be is incorporated in Mg-doped GaN, a (H-Mg Ga) may release a H + cation at relatively elevated temperatures. Consequently, the H + diffuses swiftly away from a Mg -Ga, across a barrier of 1.17 eV, towards a Be -Ga and forms a stable (H-Be Ga) with it. The activation of Mg acceptors can be thus facilitated. In this view, the process of hydrogen depassivation of the Mg acceptor by Be can convert the as-grown high-resistivity Mg-doped GaN into a p-conducting material, as observed in the experiments.

Diffusion of hydrous species in model basaltic melt

NASA Astrophysics Data System (ADS)

Zhang, Li; Guo, Xuan; Wang, Qinxia; Ding, Jiale; Ni, Huaiwei

2017-10-01

Water diffusion in Fe-free model basaltic melt with up to 2 wt% H2O was investigated at 1658-1846 K and 1 GPa in piston-cylinder apparatus using both hydration and diffusion couple techniques. Diffusion profiles measured by FTIR are consistent with a model in which both molecular H2O (H2Om) and hydroxyl (OH) contribute to water diffusion. OH diffusivity is roughly 13% of H2Om diffusivity, showing little dependence on temperature or water concentration. Water diffusion is dominated by the motion of OH until total H2O (H2Ot) concentration reaches 1 wt%. The dependence of apparent H2Ot diffusivity on H2Ot concentration appears to be overestimated by a previous study on MORB melt, but H2Ot diffusivity at 1 wt% H2Ot in basaltic melt is still greater than those in rhyolitic to andesitic melts. The appreciable contribution of OH to water diffusion in basaltic melt can be explained by enhanced mobility of OH, probably associated with the development of free hydroxyl bonded with network-modifying cations, as well as higher OH concentration. Calculation based on the Nernst-Einstein equation demonstrates that OH may serve as an effective charge carrier in hydrous basaltic melt, which could partly account for the previously observed strong influence of water on electrical conductivity of basaltic melt.

Optimal Network Modularity for Information Diffusion

NASA Astrophysics Data System (ADS)

Nematzadeh, Azadeh; Ferrara, Emilio; Flammini, Alessandro; Ahn, Yong-Yeol

2014-08-01

We investigate the impact of community structure on information diffusion with the linear threshold model. Our results demonstrate that modular structure may have counterintuitive effects on information diffusion when social reinforcement is present. We show that strong communities can facilitate global diffusion by enhancing local, intracommunity spreading. Using both analytic approaches and numerical simulations, we demonstrate the existence of an optimal network modularity, where global diffusion requires the minimal number of early adopters.

Dissolution kinetics of a lunar glass simulant at 25 degrees C: the effect of pH and organic acids

NASA Technical Reports Server (NTRS)

Eick, M. J.; Grossl, P. R.; Golden, D. C.; Sparks, D. L.; Ming, D. W.

1996-01-01

The dissolution kinetics of a simulated lunar glass were examined at pH 3, 5, and 7. Additionally, the pH 7 experiments were conducted in the presence of citric and oxalic acid at concentrations of 2 and 20 mM. The organic acids were buffered at pH 7 to examine the effect of each molecule in their dissociated form. At pH 3, 5, and 7, the dissolution of the synthetic lunar glass was observed to proceed via a two-stage process. The first stage involved the parabolic release of Ca, Mg, Al, and Fe, and the linear release of Si. Dissolution was incongruent, creating a leached layer rich in Si and Ti which was verified by transmission electron microscopy (TEM). During the second stage the release of Ca, Mg, Al, and Fe was linear. A coupled diffusion/surface dissolution model was proposed for dissolution of the simulated lunar glass at pH 3, 5, and 7. During the first stage the initial release of mobile cations (i.e., Ca, Mg, Al, Fe) was limited by diffusion through the surface leached layer of the glass (parabolic release), while Si release was controlled by the hydrolysis of the Si-O-Al bonds at the glass surface (linear release). As dissolution continued, the mobile cations diffused from greater depths within the glass surface. A steady-state was then reached where the diffusion rate across the increased path lengths equalled the Si release rate from the surface. In the presence of the organic acids, the dissolution of the synthetic lunar glass proceeded by a one stage process. The release of Ca, Mg, Al, and Fe followed a parabolic relationship, while the release of Si was linear. The relative reactivity of the organic acids used in the experiments was citrate > oxalate. A thinner leached layer rich in Si/Ti, as compared to the pH experiments, was observed using TEM. Rate data suggest that the chemisorption of the organic anion to the surface silanol groups was responsible for enhanced dissolution in the presence of the organic acids. It is proposed that the increased rate of Si release is responsible for the one stage parabolic release of mobile cations and the relatively thin leached layer compared to experiments at pH 3 and 5.

Biopharmaceutical evaluation of epigallocatechin gallate-loaded cationic lipid nanoparticles (EGCG-LNs): In vivo, in vitro and ex vivo studies.

PubMed

Fangueiro, Joana F; Calpena, Ana C; Clares, Beatriz; Andreani, Tatiana; Egea, Maria A; Veiga, Francisco J; Garcia, Maria L; Silva, Amélia M; Souto, Eliana B

2016-04-11

Cationic lipid nanoparticles (LNs) have been tested for sustained release and site-specific targeting of epigallocatechin gallate (EGCG), a potential polyphenol with improved pharmacological profile for the treatment of ocular pathologies, such as age-related macular edema, diabetic retinopathy, and inflammatory disorders. Cationic EGCG-LNs were produced by double-emulsion technique; the in vitro release study was performed in a dialysis bag, followed by the drug assay using a previously validated RP-HPLC method. In vitro HET-CAM study was carried out using chicken embryos to determine the potential risk of irritation of the developed formulations. Ex vivo permeation profile was assessed using rabbit cornea and sclera isolated and mounted in Franz diffusion cells. The results show that the use of cationic LNs provides a prolonged EGCG release, following a Boltzmann sigmoidal profile. In addition, EGCG was successfully quantified in both tested ocular tissues, demonstrating the ability of these formulations to reach both anterior and posterior segment of the eye. The pharmacokinetic study of the corneal permeation showed a first order kinetics for both cationic formulations, while EGCG-cetyltrimethylammonium bromide (CTAB) LNs followed a Boltzmann sigmoidal profile and EGCG-dimethyldioctadecylammonium bromide (DDAB) LNs a first order profile. Our studies also proved the safety and non-irritant nature of the developed LNs. Thus, loading EGCG in cationic LNs is recognised as a promising strategy for the treatment of ocular diseases related to anti-oxidant and anti-inflammatory pathways. Copyright © 2016 Elsevier B.V. All rights reserved.

Evidence-based practice: how nurse leaders can facilitate innovation.

PubMed

Shirey, Maria R

2006-01-01

Evidence-based nursing practice (EBNP) is the wave of the future. Increasingly, EBNP is being identified as a key to quality and excellence in nursing services. Incorporating evidence into practice is necessary to deliver scientifically sound patient care. In addition, understanding the importance of evidence is crucial for meeting the excellence requirements of Magnet designation. Despite the growing popularity of EBNP and its documented significant benefits, the literature demonstrates that only 15% of the nursing workforce consistently practices within an EBNP framework. If EBNP adoption is to increase in the profession, it will require the active efforts of nurse leaders to pursue an aggressive innovation diffusion strategy. The purpose of this article is to discuss the nurse leader's role in facilitating EBNP in nursing using a theoretical framework grounded in innovation diffusion theory. The article develops 4 areas of focus. First, the components of innovation diffusion theory are discussed. Second, a pertinent empirical review of the EBNP adoption literature is presented. Third, strategies for applying innovation diffusion theory to facilitate EBNP adoption are proposed. Lastly, the article ends with a leadership call to action.

Studies on the System Regulating Proton Movement across the Chloroplast Envelope 1

PubMed Central

Peters, Jeanne S.; Berkowitz, Gerald A.

1991-01-01

Studies were undertaken to further characterize the spinach (Spinacea oleracea) chloroplast envelope system, which facilitates H+ movement into and out of the stroma, and, hence, modulates photosynthetic activity by regulating stromal pH. It was demonstrated that high envelope-bound Mg2+ causes stromal acidification and photosynthetic inhibition. High envelope-bound Mg2+ was also found to necessitate the activity of a digitoxinand oligomycin-sensitive ATPase for the maintenance of high stromal pH and photosynthesis in the illuminated chloroplast. In chloroplasts that had high envelope Mg2+ and inhibited envelope ATPase activity, 2-(diethylamino)-N-(2,6-dimethylphenyl)acetamide was found to raise stromal pH and stimulate photosynthesis. 2-(Diethylamino)-N-(2,6-dimethylphenyl)acetamide is an amine anesthetic that is known to act as a monovalent cation channel blocker in mammalian systems. We postulate that the system regulating cation and H+ fluxes across the plastid envelope includes a monovalent cation channel in the envelope, some degree of (envelope-bound Mg2+ modulated) H+ flux linked to monovalent cation antiport, and ATPase-dependent H+ efflux. PMID:16668116

Can Fe3+ and Al3+ ions serve as cationic bridges to facilitate the adsorption of anionic As(V) species on humic acids? A density functional theory study.

PubMed

Gorb, Leonid; Shukla, Manoj K

2017-03-01

A computational chemistry investigation was undertaken to shed light on the facilitatory role played by Fe 3+ and Al 3+ cations in the adsorption of anionic As(V) species by humic acids through the formation of so-called cationic bridges. Geometric and energetic parameters were obtained using density functional theory at the B3LYP/6-31G(d,p) level in conjunction with the polarizable continuum model (to account for the influence of bulk water). We found that, despite their similar molecular geometries, the adsorption energies of the As(V) species AsO 4 3- and H 2 AsO 4- differ when Fe 3+ , FeOH 2+ , Al 3+ , and AlOH 2+ participate in the bridge. We also found that effective adsorption of As(V) species by humic acids strongly depends on whether the considered cationic bridges are tightly coordinated by humic acids at the adsorption sites, as well as on the rigidity of these humic acid adsorption sites.

Quantification of the Intracellular Life Time of Water Molecules to Measure Transport Rates of Human Aquaglyceroporins.

PubMed

Palmgren, Madelene; Hernebring, Malin; Eriksson, Stefanie; Elbing, Karin; Geijer, Cecilia; Lasič, Samo; Dahl, Peter; Hansen, Jesper S; Topgaard, Daniel; Lindkvist-Petersson, Karin

2017-12-01

Orthodox aquaporins are transmembrane channel proteins that facilitate rapid diffusion of water, while aquaglyceroporins facilitate the diffusion of small uncharged molecules such as glycerol and arsenic trioxide. Aquaglyceroporins play important roles in human physiology, in particular for glycerol metabolism and arsenic detoxification. We have developed a unique system applying the strain of the yeast Pichia pastoris, where the endogenous aquaporins/aquaglyceroporins have been removed and human aquaglyceroporins AQP3, AQP7, and AQP9 are recombinantly expressed enabling comparative permeability measurements between the expressed proteins. Using a newly established Nuclear Magnetic Resonance approach based on measurement of the intracellular life time of water, we propose that human aquaglyceroporins are poor facilitators of water and that the water transport efficiency is similar to that of passive diffusion across native cell membranes. This is distinctly different from glycerol and arsenic trioxide, where high glycerol transport efficiency was recorded.

Voltammetry of ion transfer across a polarized room-temperature ionic liquid membrane facilitated by valinomycin: theoretical aspects and application.

PubMed

Langmaier, Jan; Samec, Zdenek

2009-08-01

Cyclic voltammetry is used to investigate the transfer of alkali-metal cations, protons, and ammonium ions facilitated by the complex formation with valinomycin at the interface between an aqueous electrolyte solution and a room-temperature ionic liquid (RTIL) membrane. The membrane is made of a thin (approximately 112 microm) microporous filter impregnated with an RTIL that is composed of tridodecylmethylammonium cations and tetrakis[3,5-bis(trifluoromethyl)phenyl]borate anions. An extension of the existing theory of voltammetry of ion transfer across polarized liquid membranes makes it possible to evaluate the standard ion-transfer potentials for the hydrophilic cations studied, as well as the stability constants (K(i)) of their 1:1 complexes with valinomycin, as log K(i) = 9.0 (H(+)), 11.1 (Li(+)), 12.8 (Na(+)), 17.2 (K(+)), 15.7 (Rb(+)), 15.1 (Cs(+)), and 14.7 (NH(4)(+)). These data point to the remarkably enhanced stability of the valinomycin complexes within RTIL, and to the enhanced selectivity of valinomycin for K(+) over all other univalent ions studied, compared to the conventional K(+) ion-selective liquid-membrane electrodes. Selective complex formation allows one to resolve voltammetric responses of K(+) and Na(+) in the presence of an excess of Mg(2+) or Ca(2+), which is demonstrated by determination of K(+) and Na(+) in the table and tap water samples.

Understanding ionic conductivity trends in polyborane solid electrolytes from ab initio molecular dynamics

NASA Astrophysics Data System (ADS)

Varley, Joel; Kweon, Kyoung; Mehta, Prateek; Shea, Patrick; Heo, Tae Wook; Stavila, Vitalie; Udovic, Terrence; Wood, Brandon

Polyborane salts based on B12H122- , B10H102- , and their carboborane counterparts CB11H12- and CB9H10- demonstrate extraordinary Li and Na superionic conductivity that make them attractive as electrolytes in all-solid-state batteries. Their rich chemical and structural diversity creates a versatile design space that could be used to optimize materials with even higher conductivity at lower temperatures; however, many mechanistic details remain enigmatic, including reasons why certain modifications lead to improved performance. Here, we use extensive ab initio molecular dynamics simulations to broadly explore the dependence of ionic conductivity on cation/anion pair combinations for Li and Na polyborane salts. Further simulations based on Li2B12H12 as a model system are used to probe the additional influence of local perturbations, including modifications to chemistry, stoichiometry, and composition. Carbon doping, anion alloying, and cation off-stoichiometry are found to be favorable because they introduce intrinsic disorder, which facilitates local deviations from the expected cation population. Anion reorientations are also discovered to be critical for conduction, with benefits associated with lattice expansion traceable to the facilitation of anion rotation at larger volumes. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

On time-dependent diffusion coefficients arising from stochastic processes with memory

NASA Astrophysics Data System (ADS)

Carpio-Bernido, M. Victoria; Barredo, Wilson I.; Bernido, Christopher C.

2017-08-01

Time-dependent diffusion coefficients arise from anomalous diffusion encountered in many physical systems such as protein transport in cells. We compare these coefficients with those arising from analysis of stochastic processes with memory that go beyond fractional Brownian motion. Facilitated by the Hida white noise functional integral approach, diffusion propagators or probability density functions (pdf) are obtained and shown to be solutions of modified diffusion equations with time-dependent diffusion coefficients. This should be useful in the study of complex transport processes.

Synthesis of nanopowders of the aluminum-substituted lanthanum gallate solid electrolyte by mechanochemical route

NASA Astrophysics Data System (ADS)

Domingues, Eddy M.; Gonçalves, Priscila; Figueiredo, Filipe M.

2012-07-01

The room temperature mechanosynthesis of La1-xSrxGa1-y-zMgyAlzO3-δ nanopowders is successfully demonstrated for a broad compositional range (x ≤ 0.1; y ≤ 0.2, z ≤ 0.4) by resorting to a nearly amorphous alumina precursor with enhanced reactivity. It is shown that ceramics with one single phase and free from open porosity can be obtained by sintering these nanopowders at 1350-1450 °C. Microstructural data show that the substitution of Ga by Al hinders densification and decreases the grain size of ceramics. This is explained assuming the segregation of aluminum cations to the grain boundaries as a result of the decrease of the cationic diffusion coefficients.

Characterization, production, and purification of carnocin H, a bacteriocin produced by Carnobacterium 377.

PubMed

Blom, H; Katla, T; Nissen, H; Holo, H

2001-10-01

Carnocin H, a bacteriocin produced by a Carnobacterium sp., inhibited lactic acid bacteria, clostridia, enterococci, and some Staphylococcus aureus strains. Some strains of Listeria and Pediococcus were also sensitive to carnocin H. The bacteriocin was produced during the late stationary growth phase. Carnocin H was purified by cation exchange chromatography and reverse phase chromatography. Amino acid sequence and composition indicate that carnocin H is a novel bacteriocin belonging to the class II bacteriocins. The bacteriocin consists of approximately 75 amino acid residues with a highly cationic N-terminal containing six succeeding lysines. Activity, as measured by agar diffusion zones, was reduced at increased pH values, levels of indicator bacteria, NaCl, agar, and soy oil.

Machine Learning Based Dimensionality Reduction Facilitates Ligand Diffusion Paths Assessment: A Case of Cytochrome P450cam.

PubMed

Rydzewski, J; Nowak, W

2016-04-12

In this work we propose an application of a nonlinear dimensionality reduction method to represent the high-dimensional configuration space of the ligand-protein dissociation process in a manner facilitating interpretation. Rugged ligand expulsion paths are mapped into 2-dimensional space. The mapping retains the main structural changes occurring during the dissociation. The topological similarity of the reduced paths may be easily studied using the Fréchet distances, and we show that this measure facilitates machine learning classification of the diffusion pathways. Further, low-dimensional configuration space allows for identification of residues active in transport during the ligand diffusion from a protein. The utility of this approach is illustrated by examination of the configuration space of cytochrome P450cam involved in expulsing camphor by means of enhanced all-atom molecular dynamics simulations. The expulsion trajectories are sampled and constructed on-the-fly during molecular dynamics simulations using the recently developed memetic algorithms [ Rydzewski, J.; Nowak, W. J. Chem. Phys. 2015 , 143 ( 12 ), 124101 ]. We show that the memetic algorithms are effective for enforcing the ligand diffusion and cavity exploration in the P450cam-camphor complex. Furthermore, we demonstrate that machine learning techniques are helpful in inspecting ligand diffusion landscapes and provide useful tools to examine structural changes accompanying rare events.

Treatment of boundary conditions in through-diffusion: A case study of (85)Sr(2+) diffusion in compacted illite.

PubMed

Glaus, M A; Aertsens, M; Maes, N; Van Laer, L; Van Loon, L R

2015-01-01

Valuable techniques to measure effective diffusion coefficients in porous media are an indispensable prerequisite for a proper understanding of the migration of chemical-toxic and radioactive micropollutants in the subsurface and geosphere. The present article discusses possible pitfalls and difficulties in the classical through-diffusion technique applied to situations where large diffusive fluxes of cations in compacted clay minerals or clay rocks occur. The results obtained from a benchmark study, in which the diffusion of (85)Sr(2+) tracer in compacted illite has been studied using different experimental techniques, are presented. It is shown that these techniques may yield valuable results provided that an appropriate model is used for numerical simulations. It is further shown that effective diffusion coefficients may be systematically underestimated when the concentration at the downstream boundary is not taken adequately into account in modelling, even for very low concentrations. A criterion is derived for quasi steady-state situations, by which it can be decided whether the simplifying assumption of a zero-concentration at the downstream boundary in through-diffusion is justified or not. The application of the criterion requires, however, knowledge of the effective diffusion coefficient of the clay sample. Such knowledge is often absent or only approximately available during the planning phase of a diffusion experiment. Copyright © 2015 Elsevier B.V. All rights reserved.

Electronic spectra of the tetraphenylcyclobutadienecyclopentadienylnickel(II) cation and radical

DOE PAGES

Peter R. Craig; Miller, John R.; Havlas, Zdenek; ...

2016-05-02

In this study, properties of the tetraphenylcyclobutadienecyclopentadienylnickel(II) cation 1 and its tetra-o-fluoro derivative 1a have been measured and calculated. The B3LYP/TZP optimized geometry of the free cation 1 agrees with a single-crystal X-ray diffraction structure except that in the crystal one of the phenyl substituents is strongly twisted to permit a close-packing interaction of two of its hydrogens with a nearby BF – 4 anion. The low-energy parts of the solution electronic absorption and magnetic circular dichroism (MCD) spectra of 1 and 1a have been interpreted by comparison with TD-DFT (B3LYP/TZP) results. Reduction or pulse radiolysis lead to a neutralmore » 19-electron radical, whose visible absorption and MCD spectra have been recorded and interpreted as well. The reduction is facilitated by ~0.1 V upon going from 1 to 1a« less

Extraction and characterization of ternary complexes between natural organic matter, cations, and oxyanions from a natural soil.

PubMed

Peel, Hannah R; Martin, David P; Bednar, Anthony J

2017-06-01

Natural organic matter (NOM) can have a significant influence on the mobility and fate of inorganic oxyanions, such as arsenic and selenium, in the environment. There is evidence to suggest that interactions between NOM and these oxyanions are facilitated by bridging cations (primarily Fe 3+ ) through the formation of ternary complexes. Building on previous work characterizing ternary complexes formed in the laboratory using purified NOM, this study describes the extraction and characterization of intact ternary complexes directly from a soil matrix. The complexes are stable to the basic extraction conditions (pH 12) and do not appear to change when the pH of the extract is adjusted back to neutral. The results suggest that ternary complexes between NOM, cations, and inorganic oxyanions exist in natural soils and could play a role in the speciation of inorganic oxyanions in environmental matrices. Published by Elsevier Ltd.

Photochemical Formation and Transformation of Birnessite: Effects of Cations on Micromorphology and Crystal Structure.

PubMed

Zhang, Tengfei; Liu, Lihu; Tan, WenFeng; Suib, Steven L; Qiu, Guohong; Liu, Fan

2018-05-24

As important components with excellent oxidation and adsorption activity in soils and sediments, manganese oxides affect the transportation and fate of nutrients and pollutants in natural environments. In this work, birnessite was formed by photocatalytic oxidation of Mn2+aq in the presence of nitrate under solar irradiation. The effects of concentrations and species of interlayer cations (Na+, Mg2+, and K+) on birnessite crystal structure and micromorphology were investigated. The roles of adsorbed Mn2+ and pH in the transformation of the photosynthetic birnessite were further studied. The results indicated that Mn2+aq was oxidized to birnessite by superoxide radicals (O2•-) generated from the photolysis of NO3- under UV irradiation. The particle size and thickness of birnessite decreased with increasing cation concentration. The birnessite showed a plate-like morphology in the presence of K+, while exhibited a rumpled sheet-like morphology when Na+ or Mg2+ was used. The different micromorphologies of birnessites could be ascribed to the position of cations in the interlayer. The adsorbed Mn2+ and high pH facilitated the reduction of birnessite to low-valence manganese oxides including hausmannite, feitknechtite, and manganite. This study suggests that interlayer cations and Mn2+ play essential roles in the photochemical formation and transformation of birnessite in aqueous environments.

Enhanced stability and thermoelectric figure-of-merit in copper selenide by lithium doping

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, Stephen Dongmin; Pöhls, Jan-Hendrik; Aydemir, Umut

Superionic thermoelectric materials have been shown to have high figure-of-merits, leading to expectations for efficient high-temperature thermoelectric generators. These compounds exhibit extremely high cation diffusivity, comparable to that of a liquid, which is believed to be associated with the low thermal conductivity that makes superionic materials good for thermoelectrics. However, the superionic behavior causes cation migration that leads to device deterioration, being the main obstacle for practical applications. It has been reported that lithium doping in superionic Cu2-xSe leads to suppression of the Cu ion diffusivity, but whether the material will retain the promising thermoelectric properties had not yet beenmore » investigated. Here, we report a maximum zT>1.4 from Li0.09Cu1.9Se, which is higher than what we find in the undoped samples. The high temperature effective weighted mobility of the doped sample is found higher than Cu2-xSe, while the lattice thermal conductivity remains similar. We find signatures of suppressed bipolar conduction due to an enlarged band gap. Our findings set forth a possible route for tuning the stability of superionic thermoelectric materials.« less

Adsorption of doxorubicin on citrate-capped gold nanoparticles: insights into engineering potent chemotherapeutic delivery systems

NASA Astrophysics Data System (ADS)

Curry, Dennis; Cameron, Amanda; MacDonald, Bruce; Nganou, Collins; Scheller, Hope; Marsh, James; Beale, Stefanie; Lu, Mingsheng; Shan, Zhi; Kaliaperumal, Rajendran; Xu, Heping; Servos, Mark; Bennett, Craig; Macquarrie, Stephanie; Oakes, Ken D.; Mkandawire, Martin; Zhang, Xu

2015-11-01

Gold nanomaterials have received great interest for their use in cancer theranostic applications over the past two decades. Many gold nanoparticle-based drug delivery system designs rely on adsorbed ligands such as DNA or cleavable linkers to load therapeutic cargo. The heightened research interest was recently demonstrated in the simple design of nanoparticle-drug conjugates wherein drug molecules are directly adsorbed onto the as-synthesized nanoparticle surface. The potent chemotherapeutic, doxorubicin often serves as a model drug for gold nanoparticle-based delivery platforms; however, the specific interaction facilitating adsorption in this system remains understudied. Here, for the first time, we propose empirical and theoretical evidence suggestive of the main adsorption process where (1) hydrophobic forces drive doxorubicin towards the gold nanoparticle surface before (2) cation-π interactions and gold-carbonyl coordination between the drug molecule and the cations on AuNP surface facilitate DOX adsorption. In addition, biologically relevant compounds, such as serum albumin and glutathione, were shown to enhance desorption of loaded drug molecules from AuNP at physiologically relevant concentrations, providing insight into the drug release and in vivo stability of such drug conjugates.Gold nanomaterials have received great interest for their use in cancer theranostic applications over the past two decades. Many gold nanoparticle-based drug delivery system designs rely on adsorbed ligands such as DNA or cleavable linkers to load therapeutic cargo. The heightened research interest was recently demonstrated in the simple design of nanoparticle-drug conjugates wherein drug molecules are directly adsorbed onto the as-synthesized nanoparticle surface. The potent chemotherapeutic, doxorubicin often serves as a model drug for gold nanoparticle-based delivery platforms; however, the specific interaction facilitating adsorption in this system remains understudied. Here, for the first time, we propose empirical and theoretical evidence suggestive of the main adsorption process where (1) hydrophobic forces drive doxorubicin towards the gold nanoparticle surface before (2) cation-π interactions and gold-carbonyl coordination between the drug molecule and the cations on AuNP surface facilitate DOX adsorption. In addition, biologically relevant compounds, such as serum albumin and glutathione, were shown to enhance desorption of loaded drug molecules from AuNP at physiologically relevant concentrations, providing insight into the drug release and in vivo stability of such drug conjugates. Electronic supplementary information (ESI) available: DOX-AuNP absorption spectra and colored solution images, citrate displacement data, original DOX-AuNP loading isotherm, XPS data and TEM micrographs, modelling data. See DOI: 10.1039/c5nr05826k

The cation-π interaction.

PubMed

Dougherty, Dennis A

2013-04-16

The chemistry community now recognizes the cation-π interaction as a major force for molecular recognition, joining the hydrophobic effect, the hydrogen bond, and the ion pair in determining macromolecular structure and drug-receptor interactions. This Account provides the author's perspective on the intellectual origins and fundamental nature of the cation-π interaction. Early studies on cyclophanes established that water-soluble, cationic molecules would forego aqueous solvation to enter a hydrophobic cavity if that cavity was lined with π systems. Important gas phase studies established the fundamental nature of the cation-π interaction. The strength of the cation-π interaction (Li(+) binds to benzene with 38 kcal/mol of binding energy; NH4(+) with 19 kcal/mol) distinguishes it from the weaker polar-π interactions observed in the benzene dimer or water-benzene complexes. In addition to the substantial intrinsic strength of the cation-π interaction in gas phase studies, the cation-π interaction remains energetically significant in aqueous media and under biological conditions. Many studies have shown that cation-π interactions can enhance binding energies by 2-5 kcal/mol, making them competitive with hydrogen bonds and ion pairs in drug-receptor and protein-protein interactions. As with other noncovalent interactions involving aromatic systems, the cation-π interaction includes a substantial electrostatic component. The six (four) C(δ-)-H(δ+) bond dipoles of a molecule like benzene (ethylene) combine to produce a region of negative electrostatic potential on the face of the π system. Simple electrostatics facilitate a natural attraction of cations to the surface. The trend for (gas phase) binding energies is Li(+) > Na(+) > K(+) > Rb(+): as the ion gets larger the charge is dispersed over a larger sphere and binding interactions weaken, a classical electrostatic effect. On other hand, polarizability does not define these interactions. Cyclohexane is more polarizable than benzene but a decidedly poorer cation binder. Many studies have documented cation-π interactions in protein structures, where lysine or arginine side chains interact with phenylalanine, tyrosine, or tryptophan. In addition, countless studies have established the importance of the cation-π interaction in a range of biological processes. Our work has focused on molecular neurobiology, and we have shown that neurotransmitters generally use a cation-π interaction to bind to their receptors. We have also shown that many drug-receptor interactions involve cation-π interactions. A cation-π interaction plays a critical role in the binding of nicotine to ACh receptors in the brain, an especially significant case. Other researchers have established important cation-π interactions in the recognition of the "histone code," in terpene biosynthesis, in chemical catalysis, and in many other systems.

The Cation-π Interaction

PubMed Central

DOUGHERTY, DENNIS A.

2014-01-01

CONSPECTUS The chemistry community now recognizes the cation-π interaction as a major force for molecular recognition, joining the hydrophobic effect, the hydrogen bond, and the ion pair in determining macromolecular structure and drug-receptor interactions. This Account provides the author’s perspective on the intellectual origins and fundamental nature of the cation-π interaction. Early studies on cyclophanes established that water-soluble, cationic molecules would forgo aqueous solvation to enter a hydrophobic cavity if that cavity was lined with π systems. Important gas phase studies established the fundamental nature of the cation-π interaction. The strength of the cation-π interaction – Li+ binds to benzene with 38 kcal/mol of binding energy; NH4+ with 19 kcal/mol– distinguishes it from the weaker polar-π interactions observed in the benzene dimer or water-benzene complexes. In addition to the substantial intrinsic strength of the cation-π interaction in gas phase studies, the cation-π interaction remains energetically significant in aqueous media and under biological conditions. Many studies have shown that cation-π interactions can enhance binding energies by 2 – 5 kcal/mol, making them competitive with hydrogen bonds and ion pairs in drug-receptor and protein-protein interactions. As with other noncovalent interactions involving aromatic systems, the cation-π interaction includes a substantial electrostatic component. The six (four) Cδ−–Hδ+ bond dipoles of a molecule like benzene (ethylene) combine to produce a region of negative electrostatic potential on the face of the π system. Simple electrostatics facilitate a natural attraction of cations to the surface. The trend for (gas phase) binding energies is Li+>Na+>K+>Rb+: as the ion gets larger the charge is dispersed over a larger sphere and binding interactions weaken, a classical electrostatic effect. On other hand, polarizability does not define these interactions. Cyclohexane is more polarizable than benzene, but a decidedly poorer cation binder. Many studies have documented cation-π interactions in protein structures, where Lys or Arg side chains interact with Phe, Tyr, or Trp. In addition, countless studies have established the importance of cation-π interaction in a range of biological processes. Our work has focused on molecular neurobiology, and we have shown that neurotransmitters generally use a cation-π interaction to bind to their receptors. We have also shown that many drug-receptor interactions involve cation-π interactions. A cation-π interaction plays a critical role in the binding of nicotine to ACh receptors in the brain, an especially significant case. Other researchers have established important cation-π interactions in the recognition of the “histone code,” in terpene biosynthesis, in chemical catalysis, and in many other systems. PMID:23214924

24 CFR 3280.704 - Fuel supply systems.

Code of Federal Regulations, 2012 CFR

2012-04-01

... be ventilated at top and bottom to facilitate diffusion of vapors. The compartment shall be... to permit diffusion of vapors and shall be insulated from the structural members of the body. Tanks...

24 CFR 3280.704 - Fuel supply systems.

Code of Federal Regulations, 2014 CFR

2014-04-01

... be ventilated at top and bottom to facilitate diffusion of vapors. The compartment shall be... to permit diffusion of vapors and shall be insulated from the structural members of the body. Tanks...

24 CFR 3280.704 - Fuel supply systems.

Code of Federal Regulations, 2013 CFR

2013-04-01

... be ventilated at top and bottom to facilitate diffusion of vapors. The compartment shall be... to permit diffusion of vapors and shall be insulated from the structural members of the body. Tanks...

Atmospheric CO2 enrichment and reactive nitrogen inputs interactively stimulate soil cation losses and acidification.

PubMed

Zhang, Li; Qiu, Yunpeng; Cheng, Lei; Wang, Yi; Liu, Lingli; Tu, Cong; Bowman, Dan C; Burkey, Kent O; Bian, Xinmin; Zhang, Weijian; Hu, Shuijin

2018-05-17

Reactive N inputs (Nr) may alleviate N-limitation of plant growth and are assumed to help sustain plant responses to the rising atmospheric CO2 (eCO2). However, Nr and eCO2 may elicit a cascade reaction that alters soil chemistry and nutrient availability, shifting the limiting factors of plant growth, particularly in acidic tropical and subtropical croplands with low organic matter and low nutrient cations. Yet, few have so far examined the interactive effects of Nr and eCO2 on the dynamics of soil cation nutrients and soil acidity. We investigated the cation dynamics in the plant-soil system with exposure to eCO2 and different N sources in a subtropical, acidic agricultural soil. eCO2 and Nr, alone and interactively, increased Ca2+ and Mg2+ in soil solutions or leachates in aerobic agroecosystems. eCO2 significantly reduced soil pH, and NH4+-N inputs amplified this effect, suggesting that eCO2-induced plant preference of NH4+-N and plant growth may facilitate soil acidification. This is, to our knowledge, the first direct demonstration of eCO2 enhancement of soil acidity, although other studies have previously shown that eCO2 can increase cation release into soil solutions. Together, these findings provide new insights into the dynamics of cation nutrients and soil acidity under future climatic scenarios, highlighting the urgency for more studies on plant-soil responses to climate change in acidic tropical and subtropical ecosystems.

Cuticular gas exchange by Antarctic sea spiders.

PubMed

Lane, Steven J; Moran, Amy L; Shishido, Caitlin M; Tobalske, Bret W; Woods, H Arthur

2018-04-25

Many marine organisms and life stages lack specialized respiratory structures, like gills, and rely instead on cutaneous respiration, which they facilitate by having thin integuments. This respiratory mode may limit body size, especially if the integument also functions in support or locomotion. Pycnogonids, or sea spiders, are marine arthropods that lack gills and rely on cutaneous respiration but still grow to large sizes. Their cuticle contains pores, which may play a role in gas exchange. Here, we examined alternative paths of gas exchange in sea spiders: (1) oxygen diffuses across pores in the cuticle, a common mechanism in terrestrial eggshells, (2) oxygen diffuses directly across the cuticle, a common mechanism in small aquatic insects, or (3) oxygen diffuses across both pores and cuticle. We examined these possibilities by modeling diffusive oxygen fluxes across all pores in the body of sea spiders and asking whether those fluxes differed from measured metabolic rates. We estimated fluxes across pores using Fick's law parameterized with measurements of pore morphology and oxygen gradients. Modeled oxygen fluxes through pores closely matched oxygen consumption across a range of body sizes, which means the pores facilitate oxygen diffusion. Furthermore, pore volume scaled hypermetrically with body size, which helps larger species facilitate greater diffusive oxygen fluxes across their cuticle. This likely presents a functional trade-off between gas exchange and structural support, in which the cuticle must be thick enough to prevent buckling due to external forces but porous enough to allow sufficient gas exchange. © 2018. Published by The Company of Biologists Ltd.

Diffusion kinetics of the ion exchange of benzocaine on sulfocationites

NASA Astrophysics Data System (ADS)

Al'tshuler, O. G.; Shkurenko, G. Yu.; Gorlov, A. A.; Al'tshuler, G. N.

2016-06-01

The theory of the ion exchange kinetics on strong acid cationites with the participation of weak electrolytes is discussed. The kinetics of desorption of benzocaine in the protonated and molecular forms from strong acid cationites, sulfonated polycalixarene, and KU-23 30/100 sulfocationite, is studied experimentally. It is shown that the flow of protonated benzocaine from cationite upon desorption proceeding by the ion-exchange mechanism is more intense than upon desorption of nonionized benzocaine molecules. It is established that the diffusion coefficient of benzocaine cations is (1.21 ± 0.23) × 10-12 m2/s in KU-23 30/100 sulfocation and (0.65 ± 0.06) × 10-13 m2/s in sulfonated polycalixarene, while the diffusion coefficient of benzocaine molecules is (0.65 ± 0.15) × 10-14 m2/s in sulfonated polycalixarene.

Molecular dynamics computer simulation of permeation in solids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pohl, P.I.; Heffelfinger, G.S.; Fisler, D.K.

1997-12-31

In this work the authors simulate permeation of gases and cations in solid models using molecular mechanics and a dual control volume grand canonical molecular dynamics technique. The molecular sieving nature of microporous zeolites are discussed and compared with that for amorphous silica made by sol-gel methods. One mesoporous and one microporous membrane model are tested with Lennard-Jones gases corresponding to He, H{sub 2}, Ar and CH{sub 4}. The mesoporous membrane model clearly follows a Knudsen diffusion mechanism, while the microporous model having a hard-sphere cutoff pore diameter of {approximately}3.4 {angstrom} demonstrates molecular sieving of the methane ({sigma} = 3.8more » {angstrom}) but anomalous behavior for Ar ({sigma} = 3.4 {angstrom}). Preliminary results of Ca{sup +} diffusion in calcite and He/H{sub 2} diffusion in polyisobutylene are also presented.« less

Effect of Sulfuric and Triflic Acids on the Hydration of Vanadium Cations: An ab Initio Study.

PubMed

Sepehr, Fatemeh; Paddison, Stephen J

2015-06-04

Vanadium redox flow batteries (VRFBs) may be a promising solution for large-scale energy storage applications, but the crossover of any of the redox active species V(2+), V(3+), VO(2+), and VO2(+) through the ion exchange membrane will result in self-discharge of the battery. Hence, a molecular level understanding of the states of vanadium cations in the highly acidic environment of a VRFB is needed. We examine the effects of sulfuric and triflic (CF3SO3H) acids on the hydration of vanadium species as they mimic the electrolyte and functional group of perfluorosulfonic acid (PFSA) membranes. Hybrid density functional theory in conjunction with a continuum solvation model was utilized to obtain the local structures of the hydrated vanadium cations in proximity to H2SO4, CF3SO3H, and their conjugate anions. The results indicate that none of these species covalently bond to the vanadium cations. The hydration structure of V(3+) is more distorted than that of V(2+) in an acidic medium. The oxo-group of VO2(+) is protonated by either acid, in contrast to VO(2+) which is not protonated. The atomic partial charge of the four oxidation states of vanadium varies from +1.7 to +2.0. These results provide the local solvation structures of vanadium cations in the VRFBs environment that are directly related to the electrolytes stability and diffusion of vanadium ions into the membrane.

Mixed titanium, silicon, and aluminum oxide nanostructures as novel adsorbent for removal of rhodamine 6G and methylene blue as cationic dyes from aqueous solution.

PubMed

Pal, Umapada; Sandoval, Alberto; Madrid, Sergio Isaac Uribe; Corro, Grisel; Sharma, Vivek; Mohanty, Paritosh

2016-11-01

Mixed oxide nanoparticles containing Ti, Si, and Al of 8-15 nm size range were synthesized using a combined sol-gel - hydrothermal method. Effects of composition on the structure, morphology, and optical properties of the nanoparticles were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), microRaman spectroscopy, and diffuse reflectance spectroscopy (DRS). Dye removal abilities of the nanoparticles from aqueous solutions were tested for different cationic dyes. While all the mixed oxide nanoparticles revealed high and fast adsorption of cationic dyes, the particles containing Ti and Si turned out to be the best. The adsorption kinetics and equilibrium adsorption behavior of the adsorbate - adsorbent systems could be well described by pseudo-second-order kinetics and Langmuir isotherm model, respectively. Estimated thermodynamic parameters revealed the adsorption process is spontaneous, driven mainly by the electrostatic force between the cationic dye molecules and negative charge at nanoparticle surface. Highest dye adsorption capacity (162.96 mg MB/g) of the mixed oxide nanostructures containing Ti and Si is associated to their high specific surface area, and the presence of surface Si-O(δ-) groups, in addition to the hydroxyl groups of amorphous titania. Mixed oxide nanoparticles containing 75% Ti and 25% Si seen to be the most efficient adsorbents for removing cationic dye molecules from wastewater. Copyright © 2016 Elsevier Ltd. All rights reserved.

Measurements of the streaming potential of clay soils from tropical and subtropical regions using self-made apparatus.

PubMed

Li, Zhong-Yi; Li, Jiu-Yu; Liu, Yuan; Xu, Ren-Kou

2014-09-01

The streaming potential has been wildly used in charged parallel plates, capillaries, and porous media. However, there have been few studies involving the ζ potential of clay soils based on streaming potential measurements. A laboratory apparatus was developed in this study to measure the streaming potential (ΔE) of bulk clay soils' coupling coefficient (C) and cell resistance (R) of saturated granular soil samples. Excellent linearity of ΔE versus liquid pressure (ΔP) ensured the validity of measurements. The obtained parameters of C and R can be used to calculate the ζ potential of bulk soils. The results indicated that the ζ potentials measured by streaming potential method were significantly correlated with the ζ potentials of soil colloids determined by electrophoresis (r (2) = 0.960**). Therefore, the streaming potential method can be used to study the ζ potentials of bulk clay soils. The absolute values of the ζ potentials of four soils followed the order: Ultisol from Jiangxi > Ultisol from Anhui > Oxisol from Guangdong > Oxisol from Hainan, and this was consistent with the cation exchange capacities of these soils. The type and concentration of electrolytes affected soil ζ potentials. The ζ potential became less negative with increased electrolyte concentration. The ζ potentials were more negative in monovalent than in divalent cationic electrolyte solutions because more divalent cations were distributed in the shear plane of the diffuse layer as counter-cations on the soil surfaces than monovalent cations at the same electrolyte concentration.

Electrochemical Formation of Divalent Samarium Cation and Its Characteristics in LiCl-KCl Melt.

PubMed

Bae, Sang-Eun; Jung, Tae Sub; Cho, Young-Hwan; Kim, Jong-Yun; Kwak, Kyungwon; Park, Tae-Hong

2018-06-28

The electrochemical reduction of trivalent samarium in a LiCl-KCl eutectic melt produced highly stable divalent samarium, whose electrochemical properties and electronic structure in the molten salt were investigated using cyclic voltammetry, UV-vis absorption spectroscopy, laser-induced emission spectroscopy, and density functional theory (DFT) calculations. Diffusion coefficients of Sm 2+ and Sm 3+ were electrochemically measured to be 0.92 × 10 -5 and 1.10 × 10 -5 cm 2 /s, respectively, and the standard apparent potential of the Sm 2+/3+ couple was estimated to be -0.82 V vs Ag|Ag + at 450 °C. The spectroelectrochemical study demonstrated that the redox behavior of the samarium cations obeys the Nernst equation ( E°' = -0.83 V, n = 1) and the trivalent samarium cation was successfully converted to the divalent cation having characteristic absorption bands at 380 and 530 nm with molar absorptivity values of 1470 and 810 M -1 cm -1 , respectively. Density function theory calculations for the divalent samarium complex revealed that the absorption signals originated from the 4f 6 to 4f 5 5d 1 transitions. Additionally, laser-induced emission measurements for the Sm cations in the LiCl-KCl matrix showed that the Sm 3+ ion in the LiCl-KCl melt at 450 °C emitted an orange color of fluorescence, whereas a red colored emission was observed from the Sm 2+ ion in the solidified LCl-KCl salt at room temperature.

Quantitative Characterization of Non-Classic Polarization of Cations on Clay Aggregate Stability

PubMed Central

Hu, Feinan; Li, Hang; Liu, Xinmin; Li, Song; Ding, Wuquan; Xu, Chenyang; Li, Yue; Zhu, Longhui

2015-01-01

Soil particle interactions are strongly influenced by the concentration, valence and ion species and the pH of the bulk solution, which will also affect aggregate stability and particle transport. In this study, we investigated clay aggregate stability in the presence of different alkali ions (Li+, Na+, K+, and Cs+) at concentrations from10−5 to 10−1 mol L−1. Strong specific ion effects on clay aggregate stability were observed, and showed the order Cs+>K+>Na+>Li+. We found that it was not the effects of ion size, hydration, and dispersion forces in the cation–surface interactions but strong non-classic polarization of adsorbed cations that resulted in these specific effects. In this study, the non-classic dipole moments of each cation species resulting from the non-classic polarization were estimated. By comparing non-classic dipole moments with classic values, the observed dipole moments of adsorbed cations were up to 104 times larger than the classic values for the same cation. The observed non-classic dipole moments sharply increased with decreasing electrolyte concentration. We conclude that strong non-classic polarization could significantly suppress the thickness of the diffuse layer, thereby weakening the electric field near the clay surface and resulting in improved clay aggregate stability. Even though we only demonstrated specific ion effects on aggregate stability with several alkali ions, our results indicate that these effects could be universally important in soil aggregate stability. PMID:25874864

Synthesis of Cation and Water Free Cryptomelane Type OMS-2 Cathode Materials: The Impact of Tunnel Water on Electrochemistry

DOE Office of Scientific and Technical Information (OSTI.GOV)

Poyraz, Altug S.; Huang, Jianping; Zhang, Bingjie

Cryptomelane type manganese dioxides (α-MnO 2, OMS-2) are interesting potential cathode materials due to the ability of their one dimensional (1D) tunnels to reversibly host various cations including Li +and an accessible stable 3+/4+ redox couple. Here, we synthesized metal cation free OMS-2 materials where the tunnels were occupied by only water and hydronium ions. Water was subsequently removed from the tunnels. Cation free OMS-2 and Dry-OMS-2 were used as cathodes in Li based batteries to investigate the role of tunnel water on their electrochemistry. The initial discharge capacity was higher for Dry-OMS-2 (252 mAh/g) compared to OMS-2 (194 mAh/g),more » however, after 100 cycles Dry-OMS-2 and OMS-2 delivered 137 mAh/g and 134 mAh/g, respectively. Li +ion diffusion was more facile for Dry-OMS as evidenced by rate capability, at 400 mA/g. Dry-OMS-2 delivered 135mAh/g whereas OMS-2 delivered ~115 mAh/g. This first report of the impact of tunnel water on the electrochemistry of OMS-2 type materials demonstrates that the presence of tunnel water in OMS-2 type materials negatively impacts the electrochemistry.« less

Diffusion doping in quantum dots: bond strength and diffusivity.

PubMed

Saha, Avijit; Makkar, Mahima; Shetty, Amitha; Gahlot, Kushagra; A R, Pavan; Viswanatha, Ranjani

2017-02-23

Semiconducting materials uniformly doped with optical or magnetic impurities have been useful in a number of potential applications. However, clustering or phase separation during synthesis has made this job challenging. Recently the "inside out" diffusion doping was proposed to be successful in obtaining large sized quantum dots (QDs) uniformly doped with a dilute percentage of dopant atoms. Herein, we demonstrate the use of basic physical chemistry of diffusion to control the size and concentration of the dopants within the QDs for a given transition metal ion. We have studied three parameters; the bond strength of the core molecules and the diffusion coefficient of the diffusing metal ion are found to be important while the ease of cation exchange was not highly influential in the control of size and concentration of the single domain dilute magnetic semiconductor quantum dots (DMSQDs) with diverse dopant ions M 2+ (Fe 2+ , Ni 2+ , Co 2+ , Mn 2+ ). Steady state optical emission spectra reveal that the dopants are incorporated inside the semiconducting CdS and the emission can be tuned during shell growth. We have shown that this method enables control over doping percentage and the QDs show a superior ferromagnetic response at room temperature as compared to previously reported systems.

Opposing Effects of cAMP and T259 Phosphorylation on Plasma Membrane Diffusion of the Water Channel Aquaporin-5 in Madin-Darby Canine Kidney Cells

PubMed Central

Koffman, Jennifer S.; Arnspang, Eva C.; Marlar, Saw; Nejsum, Lene N.

2015-01-01

Aquaporin-5 (AQP5) facilitates passive water transport in glandular epithelia in response to secretory stimuli via intracellular pathways involving calcium release, cAMP and protein kinase A (PKA). In epithelial plasma membranes, AQP5 may be acutely regulated to facilitate water transport in response to physiological stimuli by changes in protein modifications, interactions with proteins and lipids, nanoscale membrane domain organization, and turnover rates. Such regulatory mechanisms could potentially be associated with alteration of diffusion behavior, possibly resulting in a change in the plasma membrane diffusion coefficient of AQP5. We aimed to test the short-term regulatory effects of the above pathways, by measuring lateral diffusion of AQP5 and an AQP5 phospho-mutant, T259A, using k-space Image Correlation Spectroscopy of quantum dot- and EGFP-labeled AQP5. Elevated cAMP and PKA inhibition significantly decreased lateral diffusion of AQP5, whereas T259A mutation showed opposing effects; slowing diffusion without stimulation and increasing diffusion to basal levels after cAMP elevation. Thus, lateral diffusion of AQP5 is significantly regulated by cAMP, PKA, and T259 phosphorylation, which could be important for regulating water flow in glandular secretions. PMID:26218429

Effect of molecular exchange on water droplet size analysis as determined by diffusion NMR: The W/O/W double emulsion case.

PubMed

Vermeir, Lien; Sabatino, Paolo; Balcaen, Mathieu; Declerck, Arnout; Dewettinck, Koen; Martins, José C; Guthausen, Gisela; Van der Meeren, Paul

2016-08-01

The accuracy of the inner water droplet size determination of W/O/W emulsions upon water diffusion measurement by diffusion NMR was evaluated. The resulting droplet size data were compared to the results acquired from the diffusion measurement of a highly water soluble marker compound with low permeability in the oil layer of a W/O/W emulsion, which provide a closer representation of the actual droplet size. Differences in droplet size data obtained from water and the marker were ascribed to extra-droplet water diffusion. The diffusion data of the tetramethylammonium cation marker were measured using high-resolution pulsed field gradient NMR, whereas the water diffusion was measured using both low-resolution and high-resolution NMR. Different data analysis procedures were evaluated to correct for the effect of extra-droplet water diffusion on the accuracy of water droplet size analysis. Using the water diffusion data, the use of a low measurement temperature and diffusion delay Δ could reduce the droplet size overestimation resulting from extra-droplet water diffusion, but this undesirable effect was inevitable. Detailed analysis of the diffusion data revealed that the extra-droplet diffusion effect was due to an exchange between the inner water phase and the oil phase, rather than by exchange between the internal and external aqueous phase. A promising data analysis procedure for retrieving reliable size data consisted of the application of Einstein's diffusion law to the experimentally determined diffusion distances. This simple procedure allowed determining the inner water droplet size of W/O/W emulsions upon measurement of water diffusion by low-resolution NMR at or even above room temperature. Copyright © 2016 Elsevier Inc. All rights reserved.

How the spontaneous insertion of amphiphilic imidazolium-based cations changes biological membranes: a molecular simulation study.

PubMed

Lim, Geraldine S; Jaenicke, Stephan; Klähn, Marco

2015-11-21

The insertion of 1-octyl-3-methylimidazolium cations (OMIM(+)) from a diluted aqueous ionic liquid (IL) solution into a model of a bacterial cell membrane is investigated. Subsequently, the mutual interactions of cations inside the membrane and their combined effect on membrane properties are derived. The ionic liquid solution and the membrane model are simulated using molecular dynamics in combination with empirical force fields. A high propensity of OMIM(+) for membrane insertion is observed, with a cation concentration at equilibrium inside the membrane 47 times larger than in the solvent. Once inserted, cations exhibit a weak effective attraction inside the membrane at a distance of 1.3 nm. At this free energy minimum, negatively charged phosphates of the phospholipids are sandwiched between two OMIM(+) to form energetically favorable OMIM(+)-phosphate-OMIM(+) types of coordination. The cation-cation association free energy is 5.9 kJ mol(-1), whereas the activation barrier for dissociation is 10.1 kJ mol(-1). Subsequently, OMIM(+) are inserted into the leaflet of the membrane bilayer that represents the extracellular side. The cations are evenly distributed with mutual cation distances according to the found optimum distance of 1.3 nm. Because of the short length of the cation alkyl chains compared to lipid fatty acids, voids are generated in the hydrophobic core of the membrane. These voids disorder the fatty acids, because they enable fatty acids to curl into these empty spaces and also cause a thinning of the membrane by 0.6 nm. Additionally, the membrane density increases at its center. The presence of OMIM(+) in the membrane facilitates the permeation of small molecules such as ammonia through the membrane, which is chosen as a model case for small polar solutes. The permeability coefficient of the membrane with respect to ammonia increases substantially by a factor of seven. This increase is caused by a reduction of the involved free energy barriers, which is effected by the cations through the thinning of the membrane and favorable interactions of the delocalized OMIM(+) charge with ammonia inside the membrane. Overall, the results indicate the antimicrobial effect of amphiphilic imidazolium-based cations that are found in various common ILs. This effect is caused by an alteration of the permeability of the bacterial membrane and other property changes.

Doped Y.sub.2O.sub.3 buffer layers for laminated conductors

DOEpatents

Paranthaman, Mariappan Parans [Knoxville, TN; Schoop, Urs [Westborough, MA; Goyal, Amit [Knoxville, TN; Thieme, Cornelis Leo Hans [Westborough, MA; Verebelyi, Darren T [Oxford, MA; Rupich, Martin W [Framingham, MA

2007-08-21

A laminated conductor includes a metallic substrate having a surface, a biaxially textured buffer layer supported by the surface of the metallic substrate, the biaxially textured buffer layer comprising Y.sub.2O.sub.3 and a dopant for blocking cation diffusion through the Y.sub.2O.sub.3, and a biaxially textured conductor layer supported by the biaxially textured buffer layer.

Rotational diffusion of nondipolar and charged solutes in alkyl-substituted imidazolium triflimides: effect of C2 methylation on solute rotation.

PubMed

Prabhu, Sugosh R; Dutt, G B

2014-08-07

Rotational diffusion of a nondipolar solute 2,5-dimethyl-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (DMDPP) and a charged solute rhodamine 110 (R110) has been investigated in 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][Tf2N]) and 1-butyl-2,3-dimethylimidazolium bis(trifluoromethylsulfonyl)imide ([BMMIM][Tf2N]) to understand the influence of the C2 methylation on solute rotation. The measured reorientation times of the nondipolar solute DMDPP are similar in both the ionic liquids and follow Stokes-Einstein-Debye hydrodynamic theory with slip hydrodynamics. In contrast, rotational diffusion of the charged solute R110 in [BMIM][Tf2N] obeys stick hydrodynamics due to specific interactions with the anion of the ionic liquid. Nevertheless, the intriguing result of this study is that the reorientation times of R110 in [BMMIM][Tf2N] deviate significantly from the predictions of stick hydrodynamics, especially at ambient temperatures. The solute-solvent boundary condition parameter Cobs, which is defined as the ratio of the measured reorientation time to the one calculated using the SED theory with stick boundary condition, for R110 is lower by a factor of 2 in [BMMIM][Tf2N] compared to [BMIM][Tf2N] at 298 K. Upon increasing the temperature, Cobs gradually increases and eventually matches with that obtained in [BMIM][Tf2N] at 348 K. It has been well established that methylation of the C2 position in [BMMIM][Tf2N] switches off the main hydrogen-bonding interaction between the anion and the cation, but increases the Coulombic interactions. As a consequence of the enhanced interionic interactions between the cation and anion of the ionic liquid, specific interactions between R110 and [Tf2N] diminish leading to the faster rotation of the solute. However, such an influence is not apparent in case of DMDPP as it does not experience specific interactions with either the cation or the anion of these ionic liquids.

Chemistry of alkali cation exchanged faujasite and mesoporous NaX using alkyl halides and phosphates

NASA Astrophysics Data System (ADS)

Lee, Min-Hong

The purpose of this work was to increase the reactivity of Faujasite X (NaX) zeolite toward the reactive decontamination of materials subject to nucleophilic attack by means of zeolite cation optimization and by means of the synthesis of mesoporous Faujasite X. Primary alkyl halides and trialkyl phosphates have been the test materials on which the cation-optimized and mesoporous zeolites have been tested. In the alkali cation optimization work, reactions of methyl iodide and 1-chloropropane with alkali metal cation exchanged Faujasite zeolite X were investigated at room temperature. The reactivity of the framework and the product formation were shown to depend on zeolite framework counter-cation. A quantitative study of zeolite product formation has been carried out, primarily using solid-state NMR spectroscopy. Large alkali cations showed preference toward substitution chemistry. In contrast, alkyl halide exposed LiX and NaX zeolites underwent both substitution and elimination. Subsequently introduced water molecules led to hydrolysis of framework species that was sensitive to framework counter-cation. The mesoporous NaX zeolites work undertakes to test whether an improvement in surface chemical reactivity can be achieved by introducing mesopores into the already reactive nucleophilic microporous NaX zeolite. Incorporation of the polydiallyl dimethyl ammonium chloride (PDADMAC) template and the formation of mesopores in Faujasite X zeolite (NaX) were successful and well-characterized. The mesopores are proposed to have occurred from incorporation of the cationic PDADMAC polymer into the zeolite by compensating zeolite framework charge. Subsequent sodium cation exchange of calcined mesoporous NaX was shown to restore the chemical reactivity characteristic of as-synthesized NaX. Trialkyl organophosphorous compounds underwent substitution reactions. The reactivity of both microporous and mesoporous Faujasite zeolite X and the product formation was shown to depend on the length of the alkyl chain. Although introduced mesopores alleviated the limited reagent diffusion to reactive sites due to the microporosity of the NaX zeolites, no marked improvement in the product yields was achieved with either the 1-chloroalkanes or the trialkyl phosphates test compounds, regardless of alkyl chain length. The disappointing results have been attributed to lack of substantial net increase in the numbers of zeolite nucleophilic sites accompanying mesopore introduction.

Mixtures of the 1-ethyl-3-methylimidazolium acetate ionic liquid with different inorganic salts: insights into their interactions.

PubMed

Oliveira, Filipe S; Cabrita, Eurico J; Todorovic, Smilja; Bernardes, Carlos E S; Lopes, José N Canongia; Hodgson, Jennifer L; MacFarlane, Douglas R; Rebelo, Luís P N; Marrucho, Isabel M

2016-01-28

In this work, we explore the interactions between the ionic liquid 1-ethyl-3-methylimidazolim acetate and different inorganic salts belonging to two different cation families, those based on ammonium and others based on sodium. NMR and Raman spectroscopy are used to screen for changes in the molecular environment of the ions in the ionic liquid + inorganic salt mixtures as compared to pure ionic liquid. The ion self-diffusion coefficients are determined from NMR data, allowing the discussion of the ionicity values of the ionic liquid + inorganic salt mixtures calculated using different methods. Our data reveal that preferential interactions are established between the ionic liquid and ammonium-based salts, as opposed to sodium-based salts. Computational calculations show the formation of aggregates between the ionic liquid and the inorganic salt, which is consistent with the spectroscopic data, and indicate that the acetate anion of the ionic liquid establishes preferential interactions with the ammonium cation of the inorganic salts, leaving the imidazolium cation less engaged in the media.

Emergence of innovative properties by replacement of nitrogen atom with phosphorus atom in quaternary ammonium ionic liquids: Insights from ab initio calculations and MD simulations

NASA Astrophysics Data System (ADS)

Ghatee, Mohammad Hadi; Bahrami, Maryam

2017-06-01

We investigate to contrasting structure, dynamic and thermophysical properties of quaternary ammonium and phosphonium ionic liquids (ILs) based on triethylalkylammonium [N222n]+ and triethylalkylphosphonium [P222n]+ cations (n = 5, 8, 12) and (bis(trifluoromethylsulfonyl)imide) anion [NTf2]- by quantum chemical calculations (QCC) and molecular dynamics (MD) simulations. QCCs conform to previous studies, showing that phosphonium cation alkyl chain rotational-energy-barrier is lower than ammonium cation. These molecular nature leads to no appreciable differences in their liquid density. However, their simulated transport properties (self-diffusion, conductivity, etc) are appreciably different. In particular, viscosity of phosphoniums are much lower than ammoniums. Ammoniums make nano-scale structural domains larger than phosphoniums. Employed analysis, vector re-orientational dynamics, ion-pair lifetime and nanostructure domain are in favor of faster dynamic for phosphoniums than ammoniums. [NTf2]- anion features a long lived pairing with ammoniums than phosphoniums. Overall, phosphoniums possess higher transference number, higher conductivity, and appreciably lower viscosity favorable for higher electrochemical performances.

Formulation studies on ibuprofen sodium-cationic dextran conjugate: effect on tableting and dissolution characteristics of ibuprofen.

PubMed

Abioye, Amos Olusegun; Kola-Mustapha, Adeola

2016-01-01

The effect of electrostatic interaction between ibuprofen sodium (IbS) and cationic diethylaminoethyl dextran (Ddex), on the tableting properties and ibuprofen release from the conjugate tablet was investigated. Ibuprofen exhibits poor flow, compaction (tableting) and dissolution behavior due to its hydrophobic structure, high cohesive, adhesive and viscoelastic properties therefore it was granulated with cationic Ddex to improve its compression and dissolution characteristics. Electrostatic interaction and hydrogen bonding between IbS and Ddex was confirmed with FT-IR and DSC results showed a stepwise endothermic solid-solid structural transformation from racemic to anhydrous forms between 120 and 175 °C which melted into liquid form at 208.15 °C. The broad and diffused DSC peaks of the conjugate granules as well as the disappearance of ibuprofen melting peak provided evidence for their highly amorphous state. It was evident that Ddex improved the flowability and densification of the granules and increased the mechanical and tensile strengths of the resulting tablets as the tensile strength increased from 0.67 ± 0.0172 to 1.90 ± 0.0038 MPa with increasing Ddex concentration. Both tapping and compression processes showed that the most prominent mechanism of densification were particle slippage, rearrangement and plastic deformation while fragmentation was minimized. Ddex retarded the extent of dissolution in general, indicating potentials for controlled release formulations. Multiple release mechanisms including diffusion; anomalous transport and super case II transport were noted. It was concluded that interaction between ibuprofen sodium and Ddex produced a novel formulation with improved flowability, tableting and dissolution characteristics with potential controlled drug release characteristics dictated by Ddex concentration.

Precise Composition Tailoring of Mixed-Cation Hybrid Perovskites for Efficient Solar Cells by Mixture Design Methods.

PubMed

Li, Liang; Liu, Na; Xu, Ziqi; Chen, Qi; Wang, Xindong; Zhou, Huanping

2017-09-26

Mixed anion/cation perovskites absorber has been recently implemented to construct highly efficient single junction solar cells and tandem devices. However, considerable efforts are still required to map the composition-property relationship of the mixed perovskites absorber, which is essential to facilitate device design. Here we report the intensive exploration of mixed-cation perovskites in their compositional space with the assistance of a rational mixture design (MD) methods. Different from the previous linear search of the cation ratios, it is found that by employing the MD methods, the ternary composition can be tuned simultaneously following simplex lattice designs or simplex-centroid designs, which enable significantly reduced experiment/sampling size to unveil the composition-property relationship for mixed perovskite materials and to boost the resultant device efficiency. We illustrated the composition-property relationship of the mixed perovskites in multidimension and achieved an optimized power conversion efficiency of 20.99% in the corresponding device. Moreover, the method is demonstrated to be feasible to help adjust the bandgap through rational materials design, which can be further extended to other materials systems, not limited in polycrystalline perovskites films for photovoltaic applications only.

Adsorption and release of ofloxacin from acid- and heat-treated halloysite.

PubMed

Wang, Qin; Zhang, Junping; Zheng, Yue; Wang, Aiqin

2014-01-01

Halloysite nanotube is an ideal vehicle of the controlled release of drugs. In this study, we systematically investigated the effects of acid- and heat-treatments on the physicochemical properties, structure and morphology of halloysite by XRD, FTIR, SEM and TEM. Afterwards, the adsorption and in vitro release properties of halloysite for cationic ofloxacin (OFL) were evaluated. The results indicate that HCl treatment has no influence on the crystal structure of halloysite, whereas it becomes amorphous after calcined at temperature higher than 500 °C. Both acid- and heat-treatments have no evident influence on the tubular structure of halloysite. OFL was adsorbed onto halloysite via electrostatic interaction between protonated OFL and negative halloysite surface, cation exchange as well as electrostatic interaction between the OFL-Al(3+) complexes and the negative halloysite surface. Acid-treatment facilitates the release of the adsorbed OFL compared with the natural halloysite in spite of a slight decrease of adsorption capacity. However, heat-treatment results in a sharp decrease of adsorption capacity for OFL owning to the OFL-promoted dissolution of aluminum and the disappearance of the porous structure. Although heat-treatment also facilitates release of the adsorbed OFL, the amount of OFL released is in fact less than the natural halloysite owing to the very low adsorption capacity. Thus, acid-activation is an effective protocol to improve the adsorption and release of halloysite for cationic drug molecules. Copyright © 2013 Elsevier B.V. All rights reserved.

Effect of Thenardite on the Direct Detection of Aromatic Amino Acids: Implications for the Search for Life in the Solar System

DOE Office of Scientific and Technical Information (OSTI.GOV)

C. Doc Richardson; Nancy W. Hinman; Jill R. Scott

2009-10-01

With the discovery of Na-sulfate minerals on Mars and Europa, recent studies using these minerals have focused on their ability to assist in the detection of bio/organic signatures. This study further investigates the ability of thenardite (Na2SO4) to effectively facilitate the ionization and identification of aromatic amino acids (phenylalanine, tyrosine, and tryptophan) using a technique called geomatrix-assisted laser desorption/ionization (GALDI) in conjunction with a Fourier transform mass spectrometry (FTICR-MS). This technique is based on the ability of a mineral host to facilitate the ionization and detection of bio/organic molecules. Spectra obtained from each aromatic amino acid alone and in combinationmore » with thenardite show differences in ionization mechanism and fragmentation patterns. These differences are due to chemical and structural differences between the aromatic side chains of their respective amino acid. Tyrosine and tryptophan when combined with thenardite were observed to undergo cation-attachment ([M+Na]+), due to the high alkali affinity of their aromatic side chains. Subsequent cation substitution of the carboxyl group led to formation double cation-attached peaks ([M-H+Na]Na+). In contrast, phenylalanine mixed with thenardite showed no evidence of Na+ interaction. Understanding how codeposition of amino acids with thenardite can affect the observed mass spectra is important for future exploration missions that are likely to use laser desorption mass spectrometry to search for bio/organic compounds in extraterrestrial environments.« less

Ion Transport via Structural Relaxations in Polymerized Ionic Liquids

NASA Astrophysics Data System (ADS)

Ganesan, Venkat; Mogurampelly, Santosh

We study the mechanisms underlying ion transport in poly(1-butyl-3-vinylimidazolium-hexafluorophosphate) polymer electrolytes. We consider polymer electrolytes of varying polymerized ionic liquid to ionic liquid (polyIL:IL) ratios and use atomistic molecular dynamics (MD) simulations to probe the dynamical and structural characteristics of the electrolyte. Our results reveal that anion diffusion along polymer backbone occurs primarily viathe formation and breaking of ion-pairs involving threepolymerized cationic monomers of twodifferent polymer chains. Moreover, we observe that the ionic diffusivities exhibit a direct correlation with the structural relaxation times of the ion-pairs and hydrogen bonds (H-bonds). These results provide new insights into the mechanisms underlying ion transport in polymerized ionic liquid electrolytes.

Elemental and cooperative diffusion in a liquid, supercooled liquid and glass resolved

NASA Astrophysics Data System (ADS)

Cassar, Daniel R.; Lancelotti, Ricardo F.; Nuernberg, Rafael; Nascimento, Marcio L. F.; Rodrigues, Alisson M.; Diz, Luiza T.; Zanotto, Edgar D.

2017-07-01

The diffusion mechanisms controlling viscous flow, structural relaxation, liquid-liquid phase separation, crystal nucleation, and crystal growth in multicomponent glass-forming liquids are of great interest and relevance in physics, chemistry, materials, and glass science. However, the diffusing entities that control each of these important dynamic processes are still unknown. The main objective of this work is to shed some light on this mystery, advancing the knowledge on this phenomenon. For that matter, we measured the crystal growth rates, the viscosity, and lead diffusivities in PbSiO3 liquid and glass in a wide temperature range. We compared our measured values with published data covering 16 orders of magnitude. We suggest that above a certain temperature range Td (1.2Tg-1.3Tg), crystal growth and viscous flow are controlled by the diffusion of silicon and lead. Below this temperature, crystal growth and viscous flow are more sluggish than the diffusion of silicon and lead. Therefore, Td marks the temperature where decoupling between the (measured) cationic diffusivity and the effective diffusivities calculated from viscosity and crystal growth rates occurs. We reasonably propose that the nature or size of the diffusional entities controlling viscous flow and crystal growth below Td is quite different; the slowest is the one controlling viscous flow, but both processes require cooperative movements of some larger structural units rather than jumps of only one or a few isolated atoms.

Electrochemically influenced cation inter-diffusion and Co 3O 4 formation on La 0.6Sr 0.4CoO 3 infiltrated into SOFC cathodes

DOE PAGES

Song, Xueyan; Lee, Shiwoo; Chen, Yun; ...

2015-06-18

Nanosized LSC electrocatalyst was infiltrated into a porous scaffold cathode composed of Sm 2O 3-doped CeO 2 (SDC) and La 0.6Sr 0.4Co 0.2Fe 0.8O 3-δ (LSCF) in a commercial button solid oxide fuel cell (SOFC). To understand the stability of cathodes infiltrated with LSC, the infiltrated composite cells were subjected to both electrochemical operating and thermal aging states at 750 °C for 1500 h. Nanostructure and local chemistry evolution of La 0.6Sr 0.4CoO 3 (LSC) infiltrated cathodes upon operation and aging were investigated by transmission electron microscopy. After operation, the LSC remained a cubic perovskite, and the crystal grains exhibitmore » comparable size to as-infiltrated LSC grains. Inter-diffusion of Fe from the LSCF to a Fe-incorporated LSC layer developed on the LSCF backbone. However, only sharp interfaces were observed between LSC and SDC backbone in the as-infiltrated cathode and such interfaces remain after operation. The infiltrated LSC on the SDC backbone also retains granular particle morphology. Furthermore, newly grown Co 3O 4 nanocrystals were found in the operated cathode. After thermal aging, on the other hand, cation inter-diffusion across the interfaces of the infiltrate particles and the cathode backbones is less than that from the operated cells. Lastly, the following hypothesis is proposed: Co 3O 4 forms on LSC arising from local charge balancing between cobalt and oxygen vacancies.« less

Protein diffusion along DNA: on the effect of roadblocks and crowders

NASA Astrophysics Data System (ADS)

Krepel, Dana; Levy, Yaakov

2016-12-01

Rapid recognition by a protein of its DNA target site is achieved through a combination of one- and three-dimensional (1D and 3D) diffusion, which allows efficient scanning of the many alternative sites. This facilitated diffusion mechanism is expected to be affected by cellular conditions, particularly crowding, given that up to 40% of the total cellular volume may by occupied by macromolecules. Both experimental and theoretical studies showed that crowding particles can enhance facilitated diffusion and accelerate search kinetics. This effect may originate from crowding forcing a trade-off between 3D and 1D diffusion. In this study, using coarse-grained molecular dynamic simulations, we investigate how the molecular properties of the crowders may modulate the effect exerted by crowding on a searcher protein. We show that crowders with an affinity to the DNA are less effective search facilitators than particles whose contribution is solely entropic. Crowders that have affinity to DNA may occupy DNA sites and thereby function as obstacles or roadblocks that slow down the searcher protein, and they may also produce a smaller excluded volume effect and so reduce usage of the hopping searching mode in favor of less-effective 3D diffusion in the bulk. We discuss how strong repulsive interactions between the crowding particles themselves may affect the overall dynamics of the crowders and their excluded volume effect. Our study shows that search kinetics and its mechanism are modulated not only by salt concentration and crowding occupancy, but also by the properties of the crowding particles.

Strong Cation Exchange Chromatography in Analysis of Posttranslational Modifications: Innovations and Perspectives

PubMed Central

Edelmann, Mariola J.

2011-01-01

Strong cation exchange (SCX) chromatography has been utilized as an excellent separation technique that can be combined with reversed-phase (RP) chromatography, which is frequently used in peptide mass spectrometry. Although SCX is valuable as the second component of such two-dimensional separation methods, its application goes far beyond efficient fractionation of complex peptide mixtures. Here I describe how SCX facilitates mapping of the protein posttranslational modifications (PTMs), specifically phosphorylation and N-terminal acetylation. The SCX chromatography has been mainly used for enrichment of these two PTMs, but it might also be beneficial for high-throughput analysis of other modifications that alter the net charge of a peptide. PMID:22174558

The relationship between the surface composition and electrical properties of corrosion films formed on carbon steel in alkaline sour medium: an XPS and EIS study.

PubMed

Galicia, Policarpo; Batina, Nikola; González, Ignacio

2006-07-27

This work studies the evolution of 1018 carbon steel surfaces during 3-15 day immersion in alkaline sour medium 0.1 M (NH4)2S and 10 ppm CN(-) as (NaCN). During this period of time, surfaces were jointly characterized by electrochemical techniques in situ (electrochemical impedance spectroscopy, EIS) and spectroscopic techniques ex situ (X-ray photoelectron spectroscopy, XPS). The results obtained by these techniques allowed for a description of electrical and chemical properties of the films of corrosion products formed at the 1018 steel surface. There is an interconversion cycle of chemical species that form films of corrosion products whose conversion reactions favor two different types of diffusions inside the films: a chemical diffusion of iron cations and a typical diffusion of atomic hydrogen. These phenomena jointly control the passivity of the interface attacked by the corrosive medium.

Ionic-to-Electronic Conductivity Crossover in CdTe-AgI-As2Te3 Glasses: An 110mAg Tracer Diffusion Study.

PubMed

Kassem, M; Alekseev, I; Bokova, M; Le Coq, D; Bychkov, E

2018-04-12

Conductivity isotherms of (CdTe) x (AgI) 0.5- x/2 (As 2 Te 3 ) 0.5- x/2 glasses (0.0 ≤ x ≤ 0.15) reveal a nonmonotonic behavior with increasing CdTe content reminiscent of mixed cation effect in oxide and chalcogenide glasses. Nevertheless, the apparent similarity appears to be partly incorrect. Using 110m Ag tracer diffusion measurements, we show that semiconducting CdTe additions produce a dual effect: (i) decreasing the Ag + ion transport by a factor of ≈200 with a simultaneous increase of the diffusion activation energy and (ii) increasing the electronic conductivity by 1.5 orders of magnitude. Consequently, the conductivity minimum at x = 0.05 reflects an ionic-to-electronic transport crossover; the silver-ion transport number decreases by 3 orders of magnitude with increasing x.

Genesis of emulsion texture due to magma mixing: a case study from Chotanagpur Granite Gneiss Complex of Eastern India

NASA Astrophysics Data System (ADS)

Gogoi, Bibhuti; Saikia, Ashima; Ahmad, Mansoor

2016-04-01

The emulsion texture is a rare magma mixing feature in which rounded bodies of one magmatic phase remain dispersed in the other coherent phase (Freundt and Schmincke, 1992). This type of special texture in hybrid rocks can significantly contribute toward understanding the mechanisms facilitating magma mixing and magma chamber dynamics involving two disparate magmas as the exact processes by which mixing occurs still remain unclear. Recent developments in microfluidics have greatly helped us to understand the complex processes governing magma mixing occurring at micro-level. Presented work uses some of the results obtained from microfluidic experiments with a view to understand the formation mechanism of emulsions preserved in the hybrid rocks of the Ghansura Rhyolite Dome (GRD) of Proterozoic Chotanagpur Granite Gneiss Complex (CGGC), Eastern India. The GRD has preserved hybrid rocks displaying emulsion texture that formed due to the interaction of a phenocryst-rich basaltic magma and host rhyolite magma. The emulsions are more or less spherical in shape and dominantly composed of amphibole having biotite rinds set in a matrix of biotite, plagioclase, K-feldspar and quartz. Amphibole compositions were determined from the core of the emulsions to the rim with a view to check for cationic substitutions. The amphibole constituting the emulsions is actinolite in composition, and commonly shows tschermakite (Ts) and pargasite (Prg) substitutions. From petrographical and mineral-chemical analyses we infer that when mafic magma, containing phenocrysts of augite, came in contact with felsic magma, diffusion of cations like H+, Al3+and others occurred from the felsic to the mafic system. These cations reacted with the clinopyroxene phenocrysts in the mafic magma to form amphibole (actinolite) crystals. The formation of amphibole crystals in the mafic system greatly increased the viscosity of the system allowing the amphibole crystals to venture into the adjacent felsic magma as veins. As these veins traversed in the felsic medium they underwent sinuous perturbations as a result of the competition between the viscous torque, due to difference in drag on each side of the veins, and the dynamic viscous bending resistance (Cubaud and Mason, 2009). Further downstream, the undulations amplified and swirls started to develop on the sinuous veins by accumulating the high viscosity mafic phase into central bulbs and depleting the regions in between them forming tails. Gradually the tails thinned out and blended into the surrounding felsic melt forming discrete viscous emulsions/swirls. After separation, the amphibole constituting the emulsions started interacting with the surrounding felsic magma forming biotite at the periphery of the emulsions. Eventually, biotite is eroded away and new rinds simultaneously form on freshly eroded surfaces of emulsions facilitating the mixing process (Farner et al., 2014). Cubaud T and Mason TG (2009) New J. Phys. 11, 075029. Farner et al. (2014) Earth and Planetary Science Letters 393, 49-59. Freundt A and Schmincke HU (1992) Contrib Mineral Petrol 112, 1-19.

Single-step assembly of cationic lipid-polymer hybrid nanoparticles for systemic delivery of siRNA.

PubMed

Yang, Xian-Zhu; Dou, Shuang; Wang, Yu-Cai; Long, Hong-Yan; Xiong, Meng-Hua; Mao, Cheng-Qiong; Yao, Yan-Dan; Wang, Jun

2012-06-26

The clinical success of therapeutics of small interfering RNA (siRNA) is still hindered by its delivery systems. Cationic polymer or lipid-based vehicles as the major delivery systems of siRNA cannot sufficiently satisfy siRNA therapeutic applications. It is hypothesized that cationic lipid-polymer hybrid nanoparticles may take advantage of both polymeric and lipid-based nanoparticles for siRNA delivery, while diminishing the shortcomings of both. In this study, cationic lipid-polymer hybrid nanoparticles were prepared by a single-step nanoprecipitation of a cationic lipid (N,N-bis(2-hydroxyethyl)-N-methyl-N-(2-cholesteryloxycarbonyl aminoethyl) ammonium bromide, BHEM-Chol) and amphiphilic polymers for systemic delivery of siRNA. The formed hybrid nanoparticles comprised a hydrophobic polylactide core, a hydrophilic poly(ethylene glycol) shell, and a cationic lipid monolayer at the interface of the core and the shell. Such hybrid nanoparticles exhibited excellent stability in serum and showed significantly improved biocompatibility compared to that of pure BHEM-Chol particles. The hybrid nanoparticles were capable of delivering siRNA into BT474 cells and facilitated the escape of loaded siRNA from the endosome into the cytoplasm. The hybrid nanoparticles carrying polo-like kinase 1 (Plk1)-specific siRNA (siPlk1) remarkably and specifically downregulated expression of the oncogene Plk1 and induced cancer cell apoptosis both in vitro and in vivo and significantly suppressed tumor growth following systemic administration. We demonstrate that this system is stable, nontoxic, highly efficient, and easy to scale up, bringing the clinical application of siRNA therapy one important step closer to reality.

Electrostatic interactions in soft particle systems: mesoscale simulations of ionic liquids.

PubMed

Wang, Yong-Lei; Zhu, You-Liang; Lu, Zhong-Yuan; Laaksonen, Aatto

2018-05-21

Computer simulations provide a unique insight into the microscopic details, molecular interactions and dynamic behavior responsible for many distinct physicochemical properties of ionic liquids. Due to the sluggish and heterogeneous dynamics and the long-ranged nanostructured nature of ionic liquids, coarse-grained meso-scale simulations provide an indispensable complement to detailed first-principles calculations and atomistic simulations allowing studies over extended length and time scales with a modest computational cost. Here, we present extensive coarse-grained simulations on a series of ionic liquids of the 1-alkyl-3-methylimidazolium (alkyl = butyl, heptyl-, and decyl-) family with Cl, [BF4], and [PF6] counterions. Liquid densities, microstructures, translational diffusion coefficients, and re-orientational motion of these model ionic liquid systems have been systematically studied over a wide temperature range. The addition of neutral beads in cationic models leads to a transition of liquid morphologies from dispersed apolar beads in a polar framework to that characterized by bi-continuous sponge-like interpenetrating networks in liquid matrices. Translational diffusion coefficients of both cations and anions decrease upon lengthening of the neutral chains in the cationic models and by enlarging molecular sizes of the anionic groups. Similar features are observed in re-orientational motion and time scales of different cationic models within the studied temperature range. The comparison of the liquid properties of the ionic systems with their neutral counterparts indicates that the distinctive microstructures and dynamical quantities of the model ionic liquid systems are intrinsically related to Coulombic interactions. Finally, we compared the computational efficiencies of three linearly scaling O(N log N) Ewald summation methods, the particle-particle particle-mesh method, the particle-mesh Ewald summation method, and the Ewald summation method based on a non-uniform fast Fourier transform technique, to calculate electrostatic interactions. Coarse-grained simulations were performed using the GALAMOST and the GROMACS packages and hardware efficiently utilizing graphics processing units on a set of extended [1-decyl-3-methylimidazolium][BF4] ionic liquid systems of up to 131 072 ion pairs.

Anisotropic diffusion at the field scale in a 4-year multi-tracer diffusion and retention experiment - I: Insights from the experimental data

NASA Astrophysics Data System (ADS)

Gimmi, Thomas; Leupin, Olivier X.; Eikenberg, Jost; Glaus, Martin A.; Van Loon, Luc R.; Waber, H. Niklaus; Wersin, Paul; Wang, Hao A. O.; Grolimund, Daniel; Borca, Camelia N.; Dewonck, Sarah; Wittebroodt, Charles

2014-01-01

Claystones are considered worldwide as barrier materials for nuclear waste repositories. In the Mont Terri underground research laboratory (URL), a nearly 4-year diffusion and retention (DR) experiment has been performed in Opalinus Clay. It aimed at (1) obtaining data at larger space and time scales than in laboratory experiments and (2) under relevant in situ conditions with respect to pore water chemistry and mechanical stress, (3) quantifying the anisotropy of in situ diffusion, and (4) exploring possible effects of a borehole-disturbed zone. The experiment included two tracer injection intervals in a borehole perpendicular to bedding, through which traced artificial pore water (APW) was circulated, and a pressure monitoring interval. The APW was spiked with neutral tracers (HTO, HDO, H2O-18), anions (Br, I, SeO4), and cations (Na-22, Ba-133, Sr-85, Cs-137, Co-60, Eu-152, stable Cs, and stable Eu). Most tracers were added at the beginning, some were added at a later stage. The hydraulic pressure in the injection intervals was adjusted according to the measured value in the pressure monitoring interval to ensure transport by diffusion only. Concentration time-series in the APW within the borehole intervals were obtained, as well as 2D concentration distributions in the rock at the end of the experiment after overcoring and subsampling which resulted in ∼250 samples and ∼1300 analyses. As expected, HTO diffused the furthest into the rock, followed by the anions (Br, I, SeO4) and by the cationic sorbing tracers (Na-22, Ba-133, Cs, Cs-137, Co-60, Eu-152). The diffusion of SeO4 was slower than that of Br or I, approximately proportional to the ratio of their diffusion coefficients in water. Ba-133 diffused only into ∼0.1 m during the ∼4 a. Stable Cs, added at a higher concentration than Cs-137, diffused further into the rock than Cs-137, consistent with a non-linear sorption behavior. The rock properties (e.g., water contents) were rather homogeneous at the centimeter scale, with no evidence of a borehole-disturbed zone. In situ anisotropy ratios for diffusion, derived for the first time directly from field data, are larger for HTO and Na-22 (∼5) than for anions (∼3-4 for Br and I). The lower ionic strength of the pore water at this location (∼0.22 M) as compared to locations of earlier experiments in the Mont Terri URL (∼0.39 M) had no notable effect on the anion accessible pore fraction for Cl, Br, and I: the value of 0.55 is within the range of earlier data. Detailed transport simulations involving different codes will be presented in a companion paper.

Effects of spin transition on diffusion of Fe2+ in ferropericlase in Earth's lower mantle

NASA Astrophysics Data System (ADS)

Saha, Saumitra; Bengtson, Amelia; Crispin, Katherine L.; van Orman, James A.; Morgan, Dane

2011-11-01

Knowledge of Fe composition in lower-mantle minerals (primarily perovskite and ferropericlase) is essential to a complete understanding of the Earth's interior. Fe cation diffusion potentially controls many aspects of the distribution of Fe in the Earth's lower mantle, including mixing of chemical heterogeneities, element partitioning, and the extent of core-mantle communications. Fe in ferropericlase has been shown to undergo a spin transition starting at about 40 GPa and exists in a mixture of high-spin and low-spin states over a wide range of pressures. Present experimental data on Fe transport in ferropericlase is limited to pressures below 35 GPa and provides little information on the pressure dependence of the activation volume and none on the impact of the spin transition on diffusion. Therefore, known experimental data on Fe diffusion cannot be reliably extrapolated to predict diffusion throughout the lower mantle. Here, first-principles and statistical modeling are combined to predict diffusion of Fe in ferropericlase over the entire lower mantle, including the effects of the Fe spin transition. A thorough statistical thermodynamic treatment is given to fully incorporate the coexistence of high- and low-spin Fe in the model of overall Fe diffusion in the lower mantle. Pure low-spin Fe diffuses approximately 104 times slower than high-spin Fe in ferropericlase but Fe diffusion of the mixed-spin state is only about 10 times slower than that of high-spin Fe. The predicted Fe diffusivities demonstrate that ferropericlase is unlikely to be rate limiting in transporting Fe in deep earth since much slower Fe diffusion in perovskite is predicted.

Design and Evaluation of a Prompting Instrument to Support Learning within the Diffusion Simulation Game

ERIC Educational Resources Information Center

Kwon, Seolim; Lara, Miguel; Enfield, Jake; Frick, Theodore

2013-01-01

Conducting an iterative usability testing, a set of prompts used as a form of instructional support was developed in order to facilitate the comprehension of the diffusion of innovations theory (Rogers, 2003) in a simulation game called the Diffusion Simulation Game (DSG) (Molenda & Rice, 1979). The six subjects who participated in the study…

Biological Effects of Short, High-Level Exposure to Gases: Sulfur Dioxide.

DTIC Science & Technology

1980-05-01

irritation and moist rales, bilaterally and anteriorly over the large bronchi. One-half of the subjects exposed to sulfur dioxide at concentrations of... burns . The pharyngeal mucosa was hyperemic but without ulceration . These men had decreased breath sounds, diffuse rales and rhonchi, with essentially...workplace have limited appli- cation in the military setting; the basis for their selection is the protection of chronically exposed workers against

A new model to study the phase transition from microstructures to nanostructures in ionic/ionic surfactants mixture.

PubMed

Sohrabi, Beheshteh; Gharibi, Hussein; Javadian, Soheila; Hashemianzadeh, Majid

2007-08-30

The phase behavior and aggregate structures of mixtures of the oppositely charged surfactants cetyltrimethyl ammonium bromide (CTAB) and sodium dodecyl sulfate (SDS) are explored at high dilution by pulsed field gradient stimulated echo (PFG-STE) NMR. The aggregation numbers and hydrodynamic radii of vesicles and mixed micelles were determined by a combination of viscosity and self-diffusion coefficient measurements. The average size of the mixed micelles was larger than that of micelles containing uniformly charged head groups. Analysis of the variations of the self-diffusion coefficient and viscosity with changing concentration of CTAB or SDS in the cationic-rich and anionic-rich regions revealed a phase transition from vesicles to mixed micelles. Differences in the lengths of the CTAB and SDS hydrophobic chains stabilize vesicles relative to other microstructures (e.g., liquid crystalline and precipitate phase), and vesicles form spontaneously over a wide range of compositions in both cationic-rich and anionic-rich solutions. The results obtained from conductometry measurements confirmed this transition. Finally, according to the capacitor model, a new model was developed for estimating the surface potentials and electrostatic free energy (g(elec)). Then we investigated the variations of electrostatic and transfer free energy in phase transition between mixed micelle and vesicle.

Interaction of cationic phthalocyanines with DNA. Importance of the structure of the substituents.

PubMed

López Zeballos, N C; Gauna, G A; García Vior, M C; Awruch, J; Dicelio, L E

2014-07-05

The interaction of novel zinc (II) cationic phthalocyanines with CT-DNA was studied using absorption and fluorescence spectroscopy, as well as thermal denaturation profiles. Results showed an electrostatic interaction between the phthalocyanines and CT-DNA. The properties of these phthalocyanines were compared taking the structure of the macrocycle peripheral substituents into account. 2,9(10),16(17),23(24)-tetrakis[(N-butyl-N-methylammonium)ethylsulfanyl]phthalocyaninatozinc(II) tetraiodide (Pc6) had a greater affinity for the CT-DNA helix than its bioisoster 2,9(10),16(17),23(24)-tetrakis[(N-dibutyl-N-methylammonium)ethoxy]phthalocyaninatozinc(II) tetraiodide (Pc7). 2,9(10),16(17),23(24)-tetrakis[(2-trimethylammonium)ethyl-sulfanyl]phthalocyaninatozinc(II) tetraiodide (Pc13) also carried a sulfur atom like Pc6, but linked to bulky substituents such as trimethylammonium groups. The planar aromatic region of the cationic phthalocyanines in this study appears to be unable to facilitate their intercalation with CT-DNA. Copyright © 2014 Elsevier B.V. All rights reserved.

Reversible changes of canavalin solubility controlled by divalent cation concentration in crude sword bean extract.

PubMed

Nishizawa, Kaho; Arii, Yasuhiro

2016-12-01

Canavalin is a vicilin-class (7S) storage protein found in sword bean (Canavalia gladiata). Our previous report indicated that canavalin is precipitated by the addition of 20 mM MgCl 2 to crude sword bean extract. Here, we examined the solubility changes induced by the addition of Mg 2+ and Ca 2+ at various concentrations. Canavalin tended to be insolubilized at relatively low concentrations of MgCl 2 (< 20 mM) and solubilized at relatively high concentrations (> 20 mM). In addition, canavalin was slightly insolubilized in the presence of NaCl. Overall, the results revealed that solubility changes are reversible and depend on the concentration of divalent cations. Therefore, we suggested a reaction scheme that describes the effects of divalent cations on the solubility of canavalin, which would facilitate the study of its physiological function and the application of canavalin in the food processing industry.

Regulation of Sodium Transport in the Inner Ear

PubMed Central

Kim, Sung Huhn; Marcus, Daniel C.

2011-01-01

Na+ concentrations in endolymph must be controlled to maintain hair cell function since the transduction channels of hair cells are cation-permeable, but not K+-selective. Flooding or fluctuations of the hair cell cytosol with Na+ would be expected to lead to cellular dysfunction, hearing loss and vertigo. This review briefly describes cellular mechanisms known to be responsible for Na+homeostasis in each compartment of the inner ear, including the cochlea, saccule, semicircular canals and endolymphatic sac. The influx of Na+into endolymph of each of the organs is likely via passive diffusion, but these pathways have not yet been identified or characterized. Na+ absorption is controlled by gate -keeper channels in the apical (endolymphatic) membrane of the transporting cells. Highly Na+-selective epithelial sodium channels (ENaC) control absorption by Reissner’s membrane, saccular extramacular epithelium, semicircular canal duct epithelium and endolymphatic sac. ENaC activity is controlled by a number of signal pathways, but most notably by genomic regulation of channel numbers in the membrane via glucocorticoid signaling. Nonselective cation channels in the apical membrane of outer sulcus epithelial cells and vestibular transitional cells mediate Na+ and parasensory K+ absorption. The K+-mediated transduction current in hair cells is also accompanied by a Na+ flux since the transduction channels are nonselective cation channels. Cation absorption by all of these cells is regulated by extracellular ATP via apical nonselective cation channels (P2X receptors). The heterogeneous population of epithelial cells in the endolymphatic sac is thought to have multiple absorptive pathways for Na+ with regulatory pathways that include glucocorticoids and purinergic agonists. PMID:21620939

VUV photo-processing of PAH cations: quantitative study on the ionization versus fragmentation processes

PubMed Central

Zhen, Junfeng; Castillo, Sarah Rodriguez; Joblin, Christine; Mulas, Giacomo; Sabbah, Hassan; Giuliani, Alexandre; Nahon, Laurent; Martin, Serge; Champeaux, Jean-Philippe; Mayer, Paul M.

2016-01-01

Interstellar polycyclic aromatic hydrocarbons (PAHs) are strongly affected by the absorption of vacuum ultraviolet (VUV) photons in the interstellar medium (ISM), yet the branching ratio between ionization and fragmentation is poorly studied. This is crucial for the stability and charge state of PAHs in the ISM in different environments, affecting in turn the chemistry, the energy balance, and the contribution of PAHs to the extinction and emission curves. We studied the interaction of PAH cations with VUV photons in the 7 – 20 eV range from the synchrotron SOLEIL beamline, DESIRS. We recorded by action spectroscopy the relative intensities of photo-fragmentation and photo-ionization for a set of eight PAH cations ranging in size from 14 to 24 carbon atoms, with different structures. At photon energies below ~13.6 eV fragmentation dominates for the smaller species, while for larger species ionization is immediately competitive after the second ionization potential (IP). At higher photon energies, all species behave similarly, the ionization yield gradually increases, leveling off between 0.8 and 0.9 at ~18 eV. Among isomers, PAH structure appears to mainly affect the fragmentation cross section, but not the ionization cross section. We also measured the second IP for all species and the third IP for two of them, all are in good agreement with theoretical ones confirming that PAH cations can be further ionized in the diffuse ISM. Determining actual PAH dication abundances in the ISM will require detailed modeling. Our measured photo-ionization yields for several PAH cations provide a necessary ingredient for such models. PMID:27212712

VUV photo-processing of PAH cations: quantitative study on the ionization versus fragmentation processes.

PubMed

Zhen, Junfeng; Castillo, Sarah Rodriguez; Joblin, Christine; Mulas, Giacomo; Sabbah, Hassan; Giuliani, Alexandre; Nahon, Laurent; Martin, Serge; Champeaux, Jean-Philippe; Mayer, Paul M

2016-05-10

Interstellar polycyclic aromatic hydrocarbons (PAHs) are strongly affected by the absorption of vacuum ultraviolet (VUV) photons in the interstellar medium (ISM), yet the branching ratio between ionization and fragmentation is poorly studied. This is crucial for the stability and charge state of PAHs in the ISM in different environments, affecting in turn the chemistry, the energy balance, and the contribution of PAHs to the extinction and emission curves. We studied the interaction of PAH cations with VUV photons in the 7 - 20 eV range from the synchrotron SOLEIL beamline, DESIRS. We recorded by action spectroscopy the relative intensities of photo-fragmentation and photo-ionization for a set of eight PAH cations ranging in size from 14 to 24 carbon atoms, with different structures. At photon energies below ~13.6 eV fragmentation dominates for the smaller species, while for larger species ionization is immediately competitive after the second ionization potential (IP). At higher photon energies, all species behave similarly, the ionization yield gradually increases, leveling off between 0.8 and 0.9 at ~18 eV. Among isomers, PAH structure appears to mainly affect the fragmentation cross section, but not the ionization cross section. We also measured the second IP for all species and the third IP for two of them, all are in good agreement with theoretical ones confirming that PAH cations can be further ionized in the diffuse ISM. Determining actual PAH dication abundances in the ISM will require detailed modeling. Our measured photo-ionization yields for several PAH cations provide a necessary ingredient for such models.

Characterizing molecular probes for diffusion measurements in the brain

PubMed Central

Kaur, Gurjinder; Hrabetova, Sabina; Guilfoyle, David N.; Nicholson, Charles; Hrabe, Jan

2008-01-01

Brain diffusion properties are at present most commonly evaluated by magnetic resonance (MR) diffusion imaging. MR cannot easily distinguish between the extracellular and intracellular signal components, but the older technique of Real-Time Iontophoresis (RTI) detects exclusively extracellular diffusion. Interpretation of the MR results would therefore benefit from auxiliary RTI measurements. This requires a molecular probe detectable by both techniques. Our aim was to specify a minimum set of requirements that such a diffusion probe should fulfill and apply it to two candidate probes: the cation tetramethylammonium (TMA+), used routinely in the RTI experiments, and the anion hexafluoroantimonate (SbF6−). Desirable characteristics of a molecular diffusion probe include predictable diffusion properties, stability, minimum interaction with cellular physiology, very slow penetration into the cells, and sufficiently strong and selective MR and RTI signals. These properties were evaluated using preparations of rat neocortical slices under normal and ischemic conditions, as well as solutions and agarose gel. While both molecules can be detected by MR and RTI, neither proved an ideal candidate. TMA+ was very stable but it penetrated into the cells and accumulated there within tens of minutes. SbF6− did not enter the cells as readily but it was not stable, particularly in ischemic tissue and at higher temperatures. Its presence also resulted in a decreased extracellular volume. These probe properties help to interpret previously published MR data on TMA+ diffusion and might play a role in other diffusion experiments obtained with them. PMID:18466980

Coupling of emergent octahedral rotations to polarization in (K,Na)NbO3 ferroelectrics.

PubMed

Levin, I; Krayzman, V; Cibin, G; Tucker, M G; Eremenko, M; Chapman, K; Paul, R L

2017-11-15

Perovskite potassium sodium niobates, K 1-x Na x NbO 3 , are promising lead-free piezoelectrics. Their dielectric and piezoelectric characteristics peak near x = 0.5, but the reasons for such property enhancement remain unclear. We addressed this uncertainty by analyzing changes in the local and average structures across the x = 0.5 composition, which have been determined using simultaneous Reverse Monte Carlo fitting of neutron and X-ray total-scattering data, potassium EXAFS, and diffuse-scattering patterns in electron diffraction. Within the A-sites, Na cations are found to be strongly off-centered along the polar axis as a result of oversized cube-octahedral cages determined by the larger K ions. These Na displacements promote off-centering of the neighboring Nb ions, so that the Curie temperature and spontaneous polarization remain largely unchanged with increasing x, despite the shrinking octahedral volumes. The enhancement of the properties near x = 0.5 is attributed to an abrupt increase in the magnitude and probability of the short-range ordered octahedral rotations, which resembles the pre-transition behavior. These rotations reduce the bond tension around Na and effectively soften the short Na-O bond along the polar axis - an effect that is proposed to facilitate reorientation of the polarization as external electric field is applied.

Atomic switches: atomic-movement-controlled nanodevices for new types of computing

PubMed Central

Hino, Takami; Hasegawa, Tsuyoshi; Terabe, Kazuya; Tsuruoka, Tohru; Nayak, Alpana; Ohno, Takeo; Aono, Masakazu

2011-01-01

Atomic switches are nanoionic devices that control the diffusion of metal cations and their reduction/oxidation processes in the switching operation to form/annihilate a metal atomic bridge, which is a conductive path between two electrodes in the on-state. In contrast to conventional semiconductor devices, atomic switches can provide a highly conductive channel even if their size is of nanometer order. In addition to their small size and low on-resistance, their nonvolatility has enabled the development of new types of programmable devices, which may achieve all the required functions on a single chip. Three-terminal atomic switches have also been developed, in which the formation and annihilation of a metal atomic bridge between a source electrode and a drain electrode are controlled by a third (gate) electrode. Three-terminal atomic switches are expected to enhance the development of new types of logic circuits, such as nonvolatile logic. The recent development of atomic switches that use a metal oxide as the ionic conductive material has enabled the integration of atomic switches with complementary metal-oxide-semiconductor (CMOS) devices, which will facilitate the commercialization of atomic switches. The novel characteristics of atomic switches, such as their learning and photosensing abilities, are also introduced in the latter part of this review. PMID:27877376

Analysis of metal tolerance in Rhizobium leguminosarum strains isolated from an ultramafic soil.

PubMed

Rubio-Sanz, Laura; Brito, Belén; Palacios, Jose

2018-02-01

Natural habitats containing high amounts of heavy metals provide a valuable source of bacteria adapted to deal with metal toxicity. A functional analysis of the population of legume endosymbiotic bacteria in an ultramafic soil was undertaken by studying a collection of Rhizobium leguminosarum bv viciae (Rlv) isolates obtained using pea as trap plant. One of the isolates, Rlv UPM1137, was selected on the basis of its higher tolerance to nickel and cobalt and presence of inducible mechanisms for such tolerance. A random transposon mutagenesis of Rlv UPM1137 allowed the generation of 14 transposant derivatives with increased nickel sensitivity; five of these transposants were also more sensitive to cobalt. Sequencing of the insertion sites revealed that one of the transposants (D2250) was affected in a gene homologous to the cation diffusion facilitator gene dmeF first identified in the metal-resistant bacterium Cupriavidus metallidurans CH34. The symbiotic performance of D2250 and two other transposants bearing single transposon insertions was unaffected under high-metal conditions, suggesting that, in contrast to previous observations in other Rlv strain, metal tolerance in UPM1137 under symbiotic conditions might be supported by functional redundancy between several mechanisms. © FEMS 2018. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.

Understanding Ammonium Transport in Bioelectrochemical Systems towards its Recovery

NASA Astrophysics Data System (ADS)

Liu, Ying; Qin, Mohan; Luo, Shuai; He, Zhen; Qiao, Rui

2016-03-01

We report an integrated experimental and simulation study of ammonia recovery using microbial electrolysis cells (MECs). The transport of various species during the batch-mode operation of an MEC was examined experimentally and the results were used to validate the mathematical model for such an operation. It was found that, while the generated electrical current through the system tends to acidify (or basify) the anolyte (or catholyte), their effects are buffered by a cascade of chemical groups such as the NH3/NH4+ group, leading to relatively stable pH values in both anolyte and catholyte. The transport of NH4+ ions accounts for ~90% of the total current, thus quantitatively confirming that the NH4+ ions serve as effective proton shuttles during MEC operations. Analysis further indicated that, because of the Donnan equilibrium at cation exchange membrane-anolyte/catholyte interfaces, the Na+ ion in the anolyte actually facilitates the transport of NH4+ ions during the early stage of a batch cycle and they compete with the NH4+ ions weakly at later time. These insights, along with a new and simple method for predicting the strength of ammonia diffusion from the catholyte toward the anolyte, will help effective design and operation of bioeletrochemical system-based ammonia recovery systems.

Potentiometric determination of trypsin using a polymeric membrane polycation-sensitive electrode based on current-controlled reagent delivery.

PubMed

Chen, Yan; Ding, Jiawang; Qin, Wei

2012-12-01

A potentiometric biosensor for the determination of trypsin is described based on current-controlled reagent delivery. A polymeric membrane protamine-sensitive electrode with dinonylnaphthalene sulfonate as cation exchanger is used for in situ generation of protamine. Diffusion of protamine across the polymeric membrane can be controlled precisely by applying an external current. The hydrolysis catalyzed with trypsin in sample solution decreases the concentration of free protamine released at the sample-membrane interface and facilitates the stripping of protamine out of the membrane surface via the ion-exchange process with sodium ions from the sample solution, thus decreasing the membrane potential, by which the protease can be sensed potentiometrically. The influences of anodic current amplitude, current pulse duration and protamine concentration in the inner filling solution on the membrane potential response have been studied. Under optimum conditions, the proposed protamine-sensitive electrode is useful for continuous and reversible detection of trypsin over the concentration range of 0.5-5UmL(-1) with a detection limit of 0.3UmL(-1). The proposed detection strategy provides a rapid and reagentless way for the detection of protease activities and offers great potential in the homogeneous immunoassays using proteases as labels. Copyright © 2012 Elsevier B.V. All rights reserved.

The role of facilitated diffusion in oxygen transport by cell-free hemoglobins: implications for the design of hemoglobin-based oxygen carriers.

PubMed

McCarthy, M R; Vandegriff, K D; Winslow, R M

2001-08-30

We compared rates of oxygen transport in an in vitro capillary system using red blood cells (RBCs) and cell-free hemoglobins. The axial PO(2) drop down the capillary was calculated using finite-element analysis. RBCs, unmodified hemoglobin (HbA(0)), cross-linked hemoglobin (alpha alpha-Hb) and hemoglobin conjugated to polyethylene-glycol (PEG-Hb) were evaluated. According to their fractional saturation curves, PEG-Hb showed the least desaturation down the capillary, which most closely matched the RBCs; HbA(0) and alpha alpha-Hb showed much greater desaturation. A lumped diffusion parameter, K*, was calculated based on the Fick diffusion equation with a term for facilitated diffusion. The overall rates of oxygen transfer are consistent with hemoglobin diffusion rates according to the Stokes-Einstein Law and with previously measured blood pressure responses in rats. This study provides a conceptual framework for the design of a 'blood substitute' based on mimicking O(2) transport by RBCs to prevent autoregulatory changes in blood flow and pressure.

Kinetics of Cation and Oxyanion Adsorption and Desorption on Ferrihydrite: Roles of Ferrihydrite Binding Sites and a Unified Model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tian, Lei; Shi, Zhenqing; Lu, Yang

Understanding the kinetics of toxic ion reactions with ferrihydrite is crucial for predicting the dynamic behavior of contaminants in soil environments. In this study, the kinetics of As(V), Cr(VI), Cu, and Pb adsorption and desorption on ferrihydrite were investigated with a combination of laboratory macroscopic experiments, microscopic investigation and mechanistic modeling. The rates of As(V), Cr(VI), Cu, and Pb adsorption and desorption on ferrihydrite, as systematically studied using a stirred-flow method, was highly dependent on the reaction pH and metal concentrations and varied significantly among four metals. Spherical aberration-corrected scanning transmission electron microscopy (Cs-STEM) showed, at sub-nano scales, all fourmore » metals were distributed within the ferrihydrite particle aggregates homogeneously after adsorption reactions, with no evidence of surface diffusion-controlled processes. Based on experimental results, we developed a unifying kinetics model for both cation and oxyanion adsorption/desorption on ferrihydrite based on the mechanistic-based equilibrium model CD-MUSIC. Overall, the model described the kinetic results well, and we quantitatively demonstrated how the equilibrium properties of the cation and oxyanion binding to various ferrihydrite sites affected the adsorption and desorption rates. Our results provided a unifying quantitative modeling method for the kinetics of both cation and oxyanion adsorption/desorption on iron minerals.« less

An optical spectrum of a large isolated gas-phase PAH cation: C78H26+

PubMed Central

Zhen, Junfeng; Mulas, Giacomo; Bonnamy, Anthony; Joblin, Christine

2016-01-01

A gas-phase optical spectrum of a large polycyclic aromatic hydrocarbon (PAH) cation - C78H26+- in the 410-610 nm range is presented. This large all-benzenoid PAH should be large enough to be stable with respect to photodissociation in the harsh conditions prevailing in the interstellar medium (ISM). The spectrum is obtained via multi-photon dissociation (MPD) spectroscopy of cationic C78H26 stored in the Fourier Transform Ion Cyclotron Resonance (FT-ICR) cell using the radiation from a mid-band optical parametric oscillator (OPO) laser. The experimental spectrum shows two main absorption peaks at 431 nm and 516 nm, in good agreement with a theoretical spectrum computed via time-dependent density functional theory (TD-DFT). DFT calculations indicate that the equilibrium geometry, with the absolute minimum energy, is of lowered, nonplanar C2 symmetry instead of the more symmetric planar D2h symmetry that is usually the minimum for similar PAHs of smaller size. This kind of slightly broken symmetry could produce some of the fine structure observed in some diffuse interstellar bands (DIBs). It can also favor the folding of C78H26+ fragments and ultimately the formation of fullerenes. This study opens up the possibility to identify the most promising candidates for DIBs amongst large cationic PAHs. PMID:26942230

Interactions of trace metals with hydrogels and filter membranes used in DET and DGT techniques.

PubMed

Garmo, Oyvind A; Davison, William; Zhang, Hao

2008-08-01

Equilibrium partitioning of trace metals between bulk solution and hydrogels/filter was studied. Under some conditions, trace metal concentrations were higher in the hydrogels or filter membranes compared to bulk solution (enrichment). In synthetic soft water, enrichment of cationic trace metals in polyacrylamide hydrogels decreased with increasing trace metal concentration. Enrichment was little affected by Ca and Mg in the concentration range typically encountered in natural freshwaters, indicating high affinity but low capacity binding of trace metals to solid structure in polyacrylamide gels. The apparent binding strength decreased in the sequence: Cu > Pb > Ni approximately to Cd approximately to Co and a low concentration of cationic Cu eliminated enrichment of weakly binding trace metal cations. The polyacrylamide gels also had an affinity for fulvic acid and/or its trace metal complexes. Enrichment of cationic Cd in agarose gel and hydrophilic polyethersulfone filter was independent of concentration (10 nM to 5 microM) but decreased with increasing Ca/ Mg concentration and ionic strength, suggesting that it is mainly due to electrostatic interactions. However, Cu and Pb were enriched even after equilibration in seawater, indicating that these metals additionally bind to sites within the agarose gel and filter. Compared to the polyacrylamide gels, agarose gel had a lower affinity for metal-fulvic complexes. Potential biases in measurements made with the diffusive equilibration in thin-films (DET) technique, identified by this work, are discussed.

The role of modifier cation field strength, oxygen speciation and network cation interaction in pressure-induced structural changes of silicate melts and glasses: 27Al, and 11B MAS NMR studies

NASA Astrophysics Data System (ADS)

Bista, S.; Stebbins, J. F.

2017-12-01

In aluminosilicate melts and glasses, both non-bridging oxygen content (NBO) and modifier cation field strength (Mg>Ca>Na>K) are known to facilitate network cation (e.g. Al, B) coordination increase with pressure. However, the role of these two compositional parameters in pressure-induced structural changes is derived from data for a limited set of compositions, where effects of the interaction between these parameters is less understood. For example, the effects of NBO are largely based on studies of Na and K aluminosilicate glasses, but effects of geologically important, higher field strength modifier cations such as Mg2+ and Fe2+ could well be significantly different. In this study, we look at a wide compositional range of Na, Ca and Mg aluminosilicate glasses (quenched from high pressure melts near to the glass transition temperature) to understand the roles of NBO and modifier cation field strength that can extend our view of processes important for silicate melts common in nature. Our results show that the role of NBO in pressure-induced structural changes varies systematically with increasing field strength of the modifier cation. In Na aluminosilicate glasses recovered from 1.5 to 3 GPa, large increases in average aluminum coordination are observed in glasses with high NBO content, while no detectable increases are seen for low nominal NBO (jadeite). In contrast, Mg aluminosilicate glasses with both high and low NBO show similar, large increases in average aluminum coordination with increasing pressure. The behaviors of Ca aluminosilicates fall between those of Na and Mg-rich glasses. We have also looked at interactions between different network forming cations in pressure-induced structural changes in low NBO Ca-aluminoborosilicate glasses with varying B/Si. Both aluminum and boron increase dramatically in coordination in these compositions 1.5 to 3 GPa. Increases in both average aluminum coordination and densification are larger in compositions containing higher boron concentrations, suggesting an interaction between boron and aluminum network cations in pressure-induced structural changes.

Diffuse sorption modeling.

PubMed

Pivovarov, Sergey

2009-04-01

This work presents a simple solution for the diffuse double layer model, applicable to calculation of surface speciation as well as to simulation of ionic adsorption within the diffuse layer of solution in arbitrary salt media. Based on Poisson-Boltzmann equation, the Gaines-Thomas selectivity coefficient for uni-bivalent exchange on clay, K(GT)(Me(2+)/M(+))=(Q(Me)(0.5)/Q(M)){M(+)}/{Me(2+)}(0.5), (Q is the equivalent fraction of cation in the exchange capacity, and {M(+)} and {Me(2+)} are the ionic activities in solution) may be calculated as [surface charge, mueq/m(2)]/0.61. The obtained solution of the Poisson-Boltzmann equation was applied to calculation of ionic exchange on clays and to simulation of the surface charge of ferrihydrite in 0.01-6 M NaCl solutions. In addition, a new model of acid-base properties was developed. This model is based on assumption that the net proton charge is not located on the mathematical surface plane but diffusely distributed within the subsurface layer of the lattice. It is shown that the obtained solution of the Poisson-Boltzmann equation makes such calculations possible, and that this approach is more efficient than the original diffuse double layer model.

Effect of the structure of imidazolium cations in [BF4](-)-type ionic liquids on direct electrochemistry and electrocatalysis of horseradish peroxidase in Nafion films.

PubMed

Lu, Lu; Huang, Xirong; Qu, Yinbo

2011-10-01

The direct electrochemistry and bioelectrocatalysis of horseradish peroxidase (HRP) in Nafion films at glassy carbon electrode (GCE) was investigated in three [BF(4)](-)-type room-temperature ionic liquids (ILs) to understand the structural effect of imidazolium cations. The three ILs are 1-ethyl-3-methylimidazolium tetrafluoroborate ([Emim][BF(4)]), 1-butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF(4)]) and 1-hexyl-3-methylimidazolium tetrafluoroborate ([Hmim][BF(4)]). A small amount of water in the three ILs is indispensable for maintaining the electrochemical activity of HRP in Nafion films, and the optimum water contents decrease with the increase of alkyl chain length on imidazole ring. Analysis shows that the optimum water contents are primarily determined by the hydrophilicity of ILs used. In contrast to aqueous medium, ILs media facilitate the direct electron transfer of HRP, and the electrochemical parameters obtained in different ILs are obviously related to the nature of ILs. The direct electron transfer between HRP and GCE is a surface-confined quasi-reversible single electron transfer process. The apparent heterogeneous electron transfer rate constant decreases gradually with the increase of alkyl chain length on imidazole ring, but the changing extent is relatively small. The electrocatalytic reduction current of H(2)O(2) at the present electrode decreases obviously with the increase of alkyl chain length, and the mass transfer of H(2)O(2) via diffusion in ILs should be responsible for the change. In addition, the modified electrode has good stability and reproducibility; the ability to tolerate high levels of F(-) has been greatly enhanced due to the use of Nafion film. When an appropriate mediator is included in the sensing layer, a sensitive nonaqueous biosensor could be fabricated. Copyright © 2011 Elsevier B.V. All rights reserved.

Electrodeionization Using Microseparated Bipolar Membranes

NASA Technical Reports Server (NTRS)

Lyons, Donald; Jackson, George; Andrews, Craig C.; Tennakoon, Charles L, K.; Singh, Waheguru; Hitchens, G. Duncan; Jabs, Harry; Chepin, James F.; Archer, Shivaun; Gonzalez-Martinez, Anukia;

Anomalous frequency-dependent ionic conductivity of lesion-laden human-brain tissue

NASA Astrophysics Data System (ADS)

Emin, David; Akhtari, Massoud; Fallah, Aria; Vinters, Harry V.; Mathern, Gary W.

2017-10-01

We study the effect of lesions on our four-electrode measurements of the ionic conductivity of (˜1 cm3) samples of human brain excised from patients undergoing pediatric epilepsy surgery. For most (˜94%) samples, the low-frequency ionic conductivity rises upon increasing the applied frequency. We attributed this behavior to the long-range (˜0.4 mm) diffusion of solvated sodium cations before encountering intrinsic impenetrable blockages such as cell membranes, blood vessels, and cell walls. By contrast, the low-frequency ionic conductivity of some (˜6%) brain-tissue samples falls with increasing applied frequency. We attribute this unusual frequency-dependence to the electric-field induced liberation of sodium cations from traps introduced by the unusually severe pathology observed in samples from these patients. Thus, the anomalous frequency-dependence of the ionic conductivity indicates trap-producing brain lesions.

The effects of charge, polymerization, and cluster size on the diffusivity of dissolved Si species in pore water

NASA Astrophysics Data System (ADS)

Yokoyama, Tadashi; Sakuma, Hiroshi

2018-03-01

Silicon (Si) is the most abundant cation in crustal rocks. The charge and degree of polymerization of dissolved Si significantly change depending on solution pH and Si concentration. We used molecular dynamics (MD) simulations to predict the self-diffusion coefficients of dissolved Si, DSi, for 15 monomeric and polymeric species at ambient temperature. The results showed that DSi decreased with increasing negative charge and increasing degree of polymerization. The relationship between DSi and charge (Z) can be expressed by DSi/10-6 = 2.0 + 9.8e0.47Z, and that between DSi and number of polymerization (NSi) by DSi/10-6 = 9.7/NSi0.56. The results also revealed that multiple Si molecules assembled into a cluster and D decreased as the cluster size increased. Experiments to evaluate the diffusivity of Si in pore water revealed that the diffusion coefficient decreased with increasing Si concentration, a result consistent with the MD simulations. Simulation results can now be used to quantitatively assess water-rock interactions and water-concrete reactions over a wide range of environmentally relevant conditions.

Sequential Introduction of Cations Deriving Large-Grain Csx FA1-x PbI3 Thin Film for Planar Hybrid Solar Cells: Insight into Phase-Segregation and Thermal-Healing Behavior.

PubMed

Huang, Jiahao; Xu, Pan; Liu, Jian; You, Xiao-Zeng

2017-03-01

Composition engineering of perovskite materials has been demonstrated to be important for high-performance solar cells. Recently, the energy favorable hybridization of formamidinium (FA) and cesium (Cs) in three dimension lead halide perovskites has been attracting increasing attention due to its potential benefit on durability. Herein, we reported a simple and effective method to produce phase-pure CsxFA1-xPbI3 thin film via sequential introduction of cations, in which the FA cation was introduced by interdiffusion annealing in the presence of N-methylimidazole (NMI). NMI was employed as an additive to slow down the crystallization and thus drive the formation of CsxFA1-xPbI3 with micrometer grain size, which probably facilitate the charge dissociation and transportation in photovoltaic devices. More importantly, composition dependent phase-segregation has been revealed and investigated for the first time during the phase-pure mixed-cation perovskites CsxFA1-xPbI3. The present findings demonstrated that suppressing phase-segregation of mixed-cation perovskites by meticulous composition engineering is significant for further development of efficient photovoltaics. It also suggested that phase-pure Cs0.15FA0.85PbI3 may be a promising candidate with superior phase-durability, which performed an efficiency over 16% in planar perovskite solar cells. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Structural, energetic, spectroscopic and QTAIM analyses of cation-π interactions involving mono- and bi-cyclic ring fused benzene systems.

PubMed

Hassan, Ayorinde; Dinadayalane, Tandabany C; Grabowski, Sławomir J; Leszczynski, Jerzy

2013-12-28

The effect of increasing the number of monocyclic six-membered rings or bicyclic rings of bicyclo[2.1.1]hexenyl fused to benzene on cation-π interactions involving alkali metal ions (Li(+), Na(+), and K(+)) has been investigated. The binding energy data at the B3LYP/6-311+G(2d,2p) level clearly indicate that the binding affinity of the metal ion with benzene is enhanced by increasing the number of rings fused irrespective of a monocyclic or a bicyclic ring. Calculated binding energies are in good agreement with the available experimental results. The binding strength of cations with ligands decreases in the order Li(+) > Na(+) > K(+). Our study establishes that trisannelation of bicyclo[2.1.1]hexene to benzene facilitates a very strong interaction between benzene and cations. Infrared (IR) frequencies and nuclear magnetic resonance (NMR) chemical shifts are shown to be valuable in characterizing cation-π interactions. The C-C bonds of the central six-membered rings are weakened due to metal ion binding. Based on the Quantum Theory of Atoms in Molecules (QTAIM), we have observed the presence of stabilizing H∙∙∙H interactions in two of the considered systems as opposed to the frequent description of these interactions as non-bonded repulsive interactions. Alkali metal ion binding with those two ligands slightly reduces the strength of such H∙∙∙H interactions.

Hierarchically assembled theranostic nanostructures for siRNA delivery and imaging applications.

PubMed

Shrestha, Ritu; Elsabahy, Mahmoud; Luehmann, Hannah; Samarajeewa, Sandani; Florez-Malaver, Stephanie; Lee, Nam S; Welch, Michael J; Liu, Yongjian; Wooley, Karen L

2012-10-24

Dual functional hierarchically assembled nanostructures, with two unique functions of carrying therapeutic cargo electrostatically and maintaining radiolabeled imaging agents covalently within separate component building blocks, have been developed via the supramolecular assembly of several spherical cationic shell cross-linked nanoparticles clustered around a central anionic shell cross-linked cylinder. The shells of the cationic nanoparticles and the hydrophobic core domain of the anionic central cylindrical nanostructure of the assemblies were utilized to complex negatively charged nucleic acids (siRNA) and to undergo radiolabeling, respectively, for potential theranostic applications. The assemblies exhibited exceptional cell transfection and radiolabeling efficiencies, providing an overall advantage over the individual components, which could each facilitate only one or the other of the functions.

Proposed quality control guidelines for antimicrobial susceptibility tests using tilmicosin.

PubMed Central

Shryock, T R; White, D W; Werner, C S; Staples, J M

1995-01-01

Quality control guidelines for tilmicosin, a novel veterinary-use-only macrolide, were developed in a multi-laboratory study according to established National Committee for Clinical Laboratory Standards (NCCLS) procedures (M23-T2). Tilmicosin was incorporated into Sensititre plates for broth microdilution endpoint testing and into two lots of 15-micrograms disks for Kirby-Bauer agar disk diffusion testing. One common lot and five unique lots of Mueller-Hinton media were used. (Broth was cation adjusted, and agar was supplemented with 5% defibrinated sheep blood.) Bacteria used for reference strains included Pasteurella haemolytica 128K, Pasteurella multocida ATCC 43137, and Staphylococcus aureus ATCC 29213 (microdilution) and ATCC 25923 (disk). Replicate tests were conducted. Disk diffusion and broth microdilution quality control ranges are proposed. PMID:7714188

K+ Stimulation of ATPase Activity Associated with the Chloroplast Inner Envelope 1

PubMed Central

Wu, Weihua; Berkowitz, Gerald A.

1992-01-01

Studies were conducted to characterize ATPase activity associated with purified chloroplast inner envelope preparations from spinach (Spinacea oleracea L.) plants. Comparison of free Mg2+ and Mg·ATP complex effects on ATPase activity revealed that any Mg2+ stimulation of activity was likely a function of the use of the Mg·ATP complex as a substrate by the enzyme; free Mg2+ may be inhibitory. In contrast, a marked (one- to twofold) stimulation of ATPase activity was noted in the presence of K+. This stimulation had a pH optimum of approximately pH 8.0, the same pH optimum found for enzyme activity in the absence of K+. K+ stimulation of enzyme activity did not follow simple Michaelis-Menton kinetics. Rather, K+ effects were consistent with a negative cooperativity-type binding of the cation to the enzyme, with the Km increasing at increasing substrate. Of the total ATPase activity associated with the chloroplast inner envelope, the K+-stimulated component was most sensitive to the inhibitors oligomycin and vanadate. It was concluded that K+ effects on this chloroplast envelope ATPase were similar to this cation's effects on other transport ATPases (such as the plasmalemma H+-ATPase). Such ATPases are thought to be indirectly involved in active K+ uptake, which can be facilitated by ATPase-dependent generation of an electrical driving force. Thus, K+ effects on the chloroplast enzyme in vitro were found to be consistent with the hypothesized role of this envelope ATPase in facilitating active cation transport in vivo. ImagesFigure 3 PMID:16668922

Comparison of the effects of divalent cations on the noradrenaline-evoked cation current in rabbit portal vein smooth muscle cells

PubMed Central

Aromolaran, A S; Large, W A

1999-01-01

The facilitatory effects of external Ca2+, Sr2+ and Ba2+ (Cao2+, Sro2+ and Bao2+) on the noradrenaline-evoked non-selective cation current (Icat) were compared in rabbit portal vein smooth muscle cells using patch pipette techniques. All divalent cations tested potentiated the amplitude of Icat and the potency sequence was Cao2+ > Sro2+ > Bao2+. Cao2+ and Sro2+ increased the amplitude of Icat by about eight times whereas Bao2+ produced only a threefold facilitation. The current-voltage relationship of Icat was not changed by Cao2+, Sro2+ or Bao2+. From noise analysis the single channel conductance (γ) was approximately 10 pS in divalent cation-free solution but was about 20 pS with Cao2+, Sro2+ and Bao2+. From noise and voltage-jump experiments it was apparent that at least three kinetically resolvable channel states are associated with Icat in divalent cation-free solution. Cao2+ and Sro2+ produced marked changes in the characteristics of the power spectrum and relaxations of Icat in response to voltage steps, consistent with a shift in the equilibrium between the channel states, whereas Bao2+ produced minimal effects. The data show that Cao2+, Sro2+ and Bao2+ increase the amplitude of Icat, which results in part from an increase in the single channel conductance. In addition the results suggest that Cao2+ and Sro2+ alter the kinetic behaviour of the single channels whereas Bao2+ has little effect on the equilibrium between the channel states. PMID:10545143

Transdermal diffusion of xenon in vitro using diffusion cells

NASA Astrophysics Data System (ADS)

Verkhovsky, A.; Petrov, E.

2015-11-01

The aim of this research was to study the diffusion rate of xenon through guinea pig skin and how viscosity of cosmetic component capryl/capric triglyceride (CCT) facilitates to deliver xenon to surface of skin patches. They were placed in Franz cell for 24 hours and diffusion rate and permeability of xenon were calculated. Thus diffusion rate was 0.031 mg/hour*cm2 and permeability was 0.003 cm/hour. Using Brookfield viscometer it was shown that viscosity of CCT decreased upon increasing xenon concentration. Obtained results can be utilized in developing of new xenon containing drugs for topical administration.

Involvement of the exomer complex in the polarized transport of Ena1 required for Saccharomyces cerevisiae survival against toxic cations

PubMed Central

Anton, Carlos; Zanolari, Bettina; Arcones, Irene; Wang, Congwei; Mulet, Jose Miguel; Spang, Anne; Roncero, Cesar

2017-01-01

Exomer is an adaptor complex required for the direct transport of a selected number of cargoes from the trans-Golgi network (TGN) to the plasma membrane in Saccharomyces cerevisiae. However, exomer mutants are highly sensitive to increased concentrations of alkali metal cations, a situation that remains unexplained by the lack of transport of any known cargoes. Here we identify several HAL genes that act as multicopy suppressors of this sensitivity and are connected to the reduced function of the sodium ATPase Ena1. Furthermore, we find that Ena1 is dependent on exomer function. Even though Ena1 can reach the plasma membrane independently of exomer, polarized delivery of Ena1 to the bud requires functional exomer. Moreover, exomer is required for full induction of Ena1 expression after cationic stress by facilitating the plasma membrane recruitment of the molecular machinery involved in Rim101 processing and activation of the RIM101 pathway in response to stress. Both the defective localization and the reduced levels of Ena1 contribute to the sensitivity of exomer mutants to alkali metal cations. Our work thus expands the spectrum of exomer-dependent proteins and provides a link to a more general role of exomer in TGN organization. PMID:29021337

Enhanced Photoreduction of Nitro-aromatic Compounds by Hydrated Electrons Derived from Indole on Natural Montmorillonite.

PubMed

Tian, Haoting; Guo, Yong; Pan, Bo; Gu, Cheng; Li, Hui; Boyd, Stephen A

2015-07-07

A new photoreduction pathway for nitro-aromatic compounds (NACs) and the underlying degradation mechanism are described. 1,3-Dinitrobenzene was reduced to 3-nitroaniline by the widely distributed aromatic molecule indole; the reaction is facilitated by montmorillonite clay mineral under both simulated and natural sunlight irradiation. The novel chemical reaction is strongly affected by the type of exchangeable cation present on montmorillonite. The photoreduction reaction is initiated by the adsorption of 1,3-dinitrobenzene and indole in clay interlayers. Under light irradiation, the excited indole molecule generates a hydrated electron and the indole radical cation. The structural negative charge of montmorillonite plausibly stabilizes the radical cation hence preventing charge recombination. This promotes the release of reactive hydrated electrons for further reductive reactions. Similar results were observed for the photoreduction of nitrobenzene. In situ irradiation time-resolved electron paramagnetic resonance and Fourier transform infrared spectroscopies provided direct evidence for the generation of hydrated electrons and the indole radical cations, which supported the proposed degradation mechanism. In the photoreduction process, the role of clay mineral is to both enhance the generation of hydrated electrons and to provide a constrained reaction environment in the galley regions, which increases the probability of contact between NACs and hydrated electrons.

Kafirin adsorption on ion-exchange resins: isotherm and kinetic studies.

PubMed

Kumar, Prashant; Lau, Pei Wen; Kale, Sandeep; Johnson, Stuart; Pareek, Vishnu; Utikar, Ranjeet; Lali, Arvind

2014-08-22

Kafirin is a natural, hydrophobic and celiac safe prolamin protein obtained from sorghum seeds. Today kafirin is found to be useful in designing delayed delivery systems and coatings of pharmaceuticals and nutraceuticals where its purity is important and this can be obtained by adsorptive chromatography. This study is the first scientific insight into the isotherm and kinetic studies of kafirin adsorption on anion- and cation-exchange resins for practical applications in preparative scale chromatography. Adsorption isotherms of kafirin were determined for five anion- and two cation-exchange resins in batch systems. Isotherm parameters such as maximum binding capacity and dissociation constant were determined from Langmuir isotherm, and adsorptive capacity and affinity constant from Freundlich isotherm. Langmuir isotherm was found to fit the adsorption equilibrium data well. Batch uptake kinetics for kafirin adsorption on these resins was also carried out and critical parameters including the diffusion coefficient, film mass transfer coefficient, and Biot number for film-pore diffusion model were calculated. Both the isotherm and the kinetic parameters were considered for selection of appropriate resin for kafirin purification. UNOsphere Q (78.26 mg/ml) and Toyopearl SP-650M (57.4 mg/ml) were found to offer better kafirin binding capacities and interaction strength with excellent uptake kinetics under moderate operating conditions. With these adsorbents, film diffusion resistance was found to be major governing factor for adsorption (Bi<10 and δ<1). Based on designer objective function, UNOsphere Q was found be best adsorbent for binding of kafirin. The data presented is valuable for designing large scale preparative adsorptive chromatographic kafirin purification systems. Copyright © 2014 Elsevier B.V. All rights reserved.

On optima: the case of myoglobin-facilitated oxygen diffusion.

PubMed

Wittenberg, Jonathan B

2007-08-15

The process of myoglobin/leghemoglobin-facilitated oxygen diffusion is adapted to function in different environments in diverse organisms. We enquire how the functional parameters of the process are optimized in particular organisms. The ligand-binding properties of the proteins, myoglobin and plant symbiotic hemoglobins, we discover, suggest that they have been adapted under genetic selection pressure for optimal performance. Since carrier-mediated oxygen transport has probably evolved independantly many times, adaptation of diverse proteins for a common functionality exemplifies the process of convergent evolution. The progenitor proteins may be built on the myoglobin scaffold or may be very different.

Ion Fluxes in Giant Excised Cardiac Membrane Patches Detected and Quantified with Ion-selective Microelectrodes

PubMed Central

Kang, Tong Mook; Markin, Vladislav S.; Hilgemann, Donald W.

2003-01-01

We have used ion-selective electrodes (ISEs) to quantify ion fluxes across giant membrane patches by measuring and simulating ion gradients on both membrane sides. Experimental conditions are selected with low concentrations of the ions detected on the membrane side being monitored. For detection from the cytoplasmic (bath) side, the patch pipette is oscillated laterally in front of an ISE. For detection on the extracellular (pipette) side, ISEs are fabricated from flexible quartz capillary tubing (tip diameters, 2–3 microns), and an ISE is positioned carefully within the patch pipette with the tip at a controlled distance from the mouth of the patch pipette. Transport activity is then manipulated by solution changes on the cytoplasmic side. Ion fluxes can be quantified by simulating the ion gradients with appropriate diffusion models. For extracellular (intrapatch pipette) recordings, ion diffusion coefficients can be determined from the time courses of concentration changes. The sensitivity and utility of the methods are demonstrated with cardiac membrane patches by measuring (a) potassium fluxes via ion channels, valinomycin, and Na/K pumps; (b) calcium fluxes mediated by Na/Ca exchangers; (c) sodium fluxes mediated by gramicidin and Na/K pumps; and (d) proton fluxes mediated by an unknown electrogenic mechanism. The potassium flux-to-current ratio for the Na/K pump is approximately twice that determined for potassium channels and valinomycin, as expected for a 3Na/2K pump stoichiometery (i.e., 2K/charge moved). For valinomycin-mediated potassium currents and gramicidin-mediated sodium currents, the ion fluxes calculated from diffusion models are typically 10–15% smaller than expected from the membrane currents. As presently implemented, the ISE methods allow reliable detection of calcium and proton fluxes equivalent to monovalent cation currents <1 pA in magnitude, and they allow detection of sodium and potassium fluxes equivalent to <5 pA currents. The capability to monitor ion fluxes, independent of membrane currents, should facilitate studies of both electrogenic and electroneutral ion–coupled transporters in giant patches. PMID:12668735

Evaluation of the antibacterial activity of a cationic polymer in aqueous solution with a convenient electrochemical method.

PubMed

Wang, Yihong; Guo, Qing; Wang, Huafu; Qian, Kun; Tian, Liang; Yao, Chen; Song, Wei; Shu, Weixia; Chen, Ping; Qi, Jinxu

2017-02-01

Quaternized chitosan is a cationic biopolymer with good antibacterial activity, biocompatibility, and biodegradability, and it has been widely applied in many fields. We have developed a convenient method to evaluate the antibacterial activity of hydroxypropyltrimethylammonium chloride chitosan (HACC) with a nonionic surfactant poloxamer in aqueous solution by monitoring the change of the oxidation peak current in cyclic voltammetry. Increasing values of the oxidation peak current were positively correlated with the antibacterial activity of HACC-poloxamer solutions. Optical microscope images, the zeta potential, and fluorescence spectroscopy showed that the aggregation state of HACC-poloxamer was related to the ratio of the two polymers and also to the antibacterial activity and oxidation peak current. At an HACC-to-poloxamer ratio of 1:0.75, the maximum surface charge density and the smooth edge of HACC-poloxamer aggregates can accelerate diffusion in aqueous solution. It is expected that this convenient method can be applied for a quick evaluation of the antibacterial activity of cationic biopolymers in aqueous solution. Graphical Abstract The cyclic voltammograms of MB in HACC/poloxamer solution, and the antibacterial efficiency against S. aureus after incubated with HACC (a) and 1/0.75 of HACC/poloxamer (b).

The structure and intermolecular forces of DNA condensates.

PubMed

Yoo, Jejoong; Aksimentiev, Aleksei

2016-03-18

Spontaneous assembly of DNA molecules into compact structures is ubiquitous in biological systems. Experiment has shown that polycations can turn electrostatic self-repulsion of DNA into attraction, yet the physical mechanism of DNA condensation has remained elusive. Here, we report the results of atomistic molecular dynamics simulations that elucidated the microscopic structure of dense DNA assemblies and the physics of interactions that makes such assemblies possible. Reproducing the setup of the DNA condensation experiments, we measured the internal pressure of DNA arrays as a function of the DNA-DNA distance, showing a quantitative agreement between the results of our simulations and the experimental data. Analysis of the MD trajectories determined the DNA-DNA force in a DNA condensate to be pairwise, the DNA condensation to be driven by electrostatics of polycations and not hydration, and the concentration of bridging cations, not adsorbed cations, to determine the magnitude and the sign of the DNA-DNA force. Finally, our simulations quantitatively characterized the orientational correlations of DNA in DNA arrays as well as diffusive motion of DNA and cations. © The Author(s) 2016. Published by Oxford University Press on behalf of Nucleic Acids Research.

The reactive element effect of ceria particle dispersion on alumina growth: A model based on microstructural observations

PubMed Central

Wang, X.; Peng, X.; Tan, X.; Wang, F.

2016-01-01

The oxidation kinetics of alumina-forming metals can be affected by adding a small amount of a reactive (normally rare earth) element oxide (RExOy) and the segregation of the reactive element (RE) ions to the growing alumina grain boundaries (GBs) has been considered as a responsible reason. However, this interpretation remains a controversial issue as to how RE ions are produced by RExOy which is thermodynamically and chemically stable in metals. The question is answered by a model that is based on transmission electron microscopy (TEM) investigation of a CeO2-dispersed nickel aluminide oxidized in air at 1100 °C. The CeO2 dispersion is incorporated into the alumina scale by the inward growth of inner α-Al2O3, where it partially dissolves producing tetravalent Ce cations which then transform to trivalent cations by trapping electrons. The trivalent cations segregate to the α-Al2O3 GBs and diffuse outward along first the GBs and later the twin boundaries (TBs) in the outer γ-Al2O3 layer, being precipitated as Ce2O3 particles near surface. PMID:27406938

Basolateral choline transport in isolated rabbit renal proximal tubules.

PubMed

Dantzler, W H; Evans, K K; Wright, S H

1998-11-01

Choline can undergo both net secretion and net reabsorption by renal proximal tubules, but at physiological plasma levels net reabsorption occurs. During this process, choline enters the cells at the luminal side down an electrochemical gradient via a specific transporter with a high affinity for choline. It appeared likely that choline was then transported out of the cells against an electrochemical gradient at the basolateral membrane by countertransport for another organic cation. This possibility was examined by studying net transepithelial reabsorption and basolateral uptake and efflux of [14C]choline in isolated S2 segments of rabbit renal proximal tubules. Basolateral uptake, which was inhibited by other organic cations such as tetraethylammonium (TEA), appeared to occur by the standard organic cation transport pathway. However, the addition of TEA to the bathing medium not only failed to trans-stimulate net transepithelial reabsorption and basolateral efflux of [14C]choline but it actually inhibited transepithelial reabsorption by @60%. The results do not support the presence of a countertransport step for choline against an electrochemical gradient at the basolateral membrane. Instead, they suggest that choline crosses this membrane by some form of carrier-mediated diffusion even during the reabsorptive process.

Cation binding at the node of Ranvier: I. Localization of binding sites during development.

PubMed

Zagoren, J C; Raine, C S; Suzuki, K

1982-06-17

Cations are known to bind to the node of Ranvier and the paranodal regions of myelinated fibers. The integrity of these specialized structures is essential for normal conduction. Sites of cation binding can be microscopically identified by the electrondense histochemical reaction product formed by the precipitate of copper sulfate/potassium ferrocyanide. This technique was used to study the distribution of cation binding during normal development of myelinating fibers. Sciatic nerves of C57B1 mice, at 1, 3, 5, 6, 7, 8, 9, 13, 16, 18, 24 and 30 days of age, were prepared for electron microscopy following fixation in phosphate-buffered 2.5% glutaraldehyde and 1% osmic acid, microdissection and incubation in phosphate-buffered 0.1 M cupric sulfate followed by 0.1 M potassium ferrocyanide. Localization of reaction product was studied by light and electron microscopy. By light microscopy, no reaction product was observed prior to 9 days of age. At 13 days, a few nodes and paranodes exhibited reaction product. This increased in frequency and intensity up to 30 days when almost all nodes or paranodes exhibited reaction product. Ultrastructurally, diffuse reaction product was first observed at 3 days of age in the axoplasm of the node, in the paranodal extracellular space of the terminal loops, in the Schwann cell proper and in the terminal loops of Schwann cell cytoplasm. When myelinated axons fulfilled the criteria for mature nodes, reaction product was no longer observed in the Schwann cell cytoplasm, while the intensity of reaction product in the nodal axoplasm and paranodal extracellular space of the terminal loops increased. Reaction product in the latter site appeared to be interrupted by the transverse bands. These results suggest that cation binding accompanies nodal maturity and that the Schwann cell may play a role in production or storage of the cation binding substance during myelinogenesis and development.

Up-regulation of K{sub ir}2.1 by ER stress facilitates cell death of brain capillary endothelial cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kito, Hiroaki; Yamazaki, Daiju; Department of Biological Chemistry, Kyoto University, Graduate School of Pharmaceutical Sciences, Kyoto

Highlights: {yields} We found that application of endoplasmic reticulum (ER) stress with tunicamycin to brain capillary endothelial cells (BCECs) induced cell death. {yields} The ER stress facilitated the expression of inward rectifier K{sup +} channel (K{sub ir}2.1) and induced sustained membrane hyperpolarization. {yields} The membrane hyperpolarization induced sustained Ca{sup 2+} entry through voltage-independent nonspecific cation channels and consequently facilitated cell death. {yields} The K{sub ir}2.1 up-regulation by ER stress is, at least in part, responsible for cell death of BCECs under pathological conditions. -- Abstract: Brain capillary endothelial cells (BCECs) form blood brain barrier (BBB) to maintain brain homeostasis. Cellmore » turnover of BCECs by the balance of cell proliferation and cell death is critical for maintaining the integrity of BBB. Here we found that stimuli with tunicamycin, endoplasmic reticulum (ER) stress inducer, up-regulated inward rectifier K{sup +} channel (K{sub ir}2.1) and facilitated cell death in t-BBEC117, a cell line derived from bovine BCECs. The activation of K{sub ir} channels contributed to the establishment of deeply negative resting membrane potential in t-BBEC117. The deep resting membrane potential increased the resting intracellular Ca{sup 2+} concentration due to Ca{sup 2+} influx through non-selective cation channels and thereby partly but significantly regulated cell death in t-BBEC117. The present results suggest that the up-regulation of K{sub ir}2.1 is, at least in part, responsible for cell death/cell turnover of BCECs induced by a variety of cellular stresses, particularly ER stress, under pathological conditions.« less

Infrared spectroscopic characterization of dehydration and accompanying phase transition behaviors in NAT-topology zeolites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Hsiu-Wen; Bishop, David

2012-01-01

Relative humidity (PH2O, partial pressure of water)-dependent dehydration and accompanying phase transitions in NAT-topology zeolites (natrolite, scolecite, and mesolite) were studied under controlled temperature and known PH2O conditions by in situ diffuse-reflectance infrared Fourier transform spectroscopy and parallel X-ray powder diffraction. Dehydration was characterized by the disappearance of internal H2O vibrational modes. The loss of H2O molecules caused a sequence of structural transitions in which the host framework transformation path was coupled primarily via the thermal motion of guest Na?/Ca2? cations and H2O molecules. The observation of different interactions of H2O molecules and Na?/Ca2? cations with host aluminosilicate frameworks undermore » highand low-PH2O conditions indicated the development of different local strain fields, arising from cation H2O interactions in NAT-type channels. These strain fields influence the Si O/Al O bond strength and tilting angles within and between tetrahedra as the dehydration temperature is approached. The newly observed infrared bands (at 2,139 cm-1 in natrolite, 2,276 cm-1 in scolecite, and 2,176 and 2,259 cm-1 in mesolite) result from strong cation H2O Al Si framework interactions in NAT-type channels, and these bands can be used to evaluate the energetic evolution of Na?/Ca2? cations before and after phase transitions, especially for scolecite and mesolite. The 2,176 and 2,259 cm-1 absorption bands in mesolite also appear to be related to Na?/Ca2? order disorder that occur when mesolite loses its Ow4 H2O molecules.« less

VUV PHOTO-PROCESSING OF PAH CATIONS: QUANTITATIVE STUDY ON THE IONIZATION VERSUS FRAGMENTATION PROCESSES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhen, Junfeng; Castillo, Sarah Rodriguez; Joblin, Christine

2016-05-10

Interstellar polycyclic aromatic hydrocarbons (PAHs) are strongly affected by the absorption of vacuum ultraviolet (VUV) photons in the interstellar medium (ISM), yet the branching ratio between ionization and fragmentation is poorly studied. This is crucial for the stability and charge state of PAHs in the ISM in different environments, affecting in turn the chemistry, the energy balance, and the contribution of PAHs to the extinction and emission curves. We studied the interaction of PAH cations with VUV photons in the 7–20 eV range from the synchrotron SOLEIL beamline, DESIRS. We recorded by action spectroscopy the relative intensities of photo-fragmentation andmore » photo-ionization for a set of eight PAH cations ranging in size from 14 to 24 carbon atoms, with different structures. At photon energies below ∼13.6 eV fragmentation dominates for the smaller species, while for larger species ionization is immediately competitive after the second ionization potential (IP). At higher photon energies all species behave similarly; the ionization yield gradually increases, leveling off between 0.8 and 0.9 at ∼18 eV. Among isomers, PAH structure appears to mainly affect the fragmentation cross section but not the ionization cross section. We also measured the second IP for all species and the third IP for two of them; all are in good agreement with theoretical ones, confirming that PAH cations can be further ionized in the diffuse ISM. Determining actual PAH dication abundances in the ISM will require detailed modeling. Our measured photo-ionization yields for several PAH cations provide a necessary ingredient for such models.« less

Single DNA molecules on freestanding and supported cationic lipid bilayers: diverse conformational dynamics controlled by the local bilayer properties

NASA Astrophysics Data System (ADS)

Herold, Christoph; Schwille, Petra; Petrov, Eugene P.

2016-02-01

We present experimental results on the interaction of DNA macromolecules with cationic lipid membranes with different properties, including freestanding membranes in the fluid and gel state, and supported lipid membranes in the fluid state and under conditions of fluid-gel phase coexistence. We observe diverse conformational dynamics of membrane-bound DNA molecules controlled by the local properties of the lipid bilayer. In case of fluid-state freestanding lipid membranes, the behaviour of DNA on the membrane is controlled by the membrane charge density: whereas DNA bound to weakly charged membranes predominantly behaves as a 2D random coil, an increase in the membrane charge density leads to membrane-driven irreversible DNA collapse and formation of subresolution-sized DNA globules. On the other hand, electrostatic binding of DNA macromolecules to gel-state freestanding membranes leads to completely arrested diffusion and conformational dynamics of membrane-adsorbed DNA. A drastically different picture is observed in case of DNA interaction with supported cationic lipid bilayers: When the supported bilayer is in the fluid state, membrane-bound DNA molecules undergo 2D translational Brownian motion and conformational fluctuations, irrespectively of the charge density of the supported bilayer. At the same time, when the supported cationic membrane shows fluid-gel phase coexistence, membrane-bound DNA molecules are strongly attracted to micrometre-sized gel-phase domains enriched with the cationic lipid, which results in 2D compaction of the membrane-bound macromolecules. This DNA compaction, however, is fully reversible, and disappears as soon as the membrane is heated above the fluid-gel coexistence. We also discuss possible biological implications of our experimental findings.

Roles of cation valance and exchange on the retention and colloid-facilitated transport of functionalized multi-walled carbon nanotubes in a natural soil

USDA-ARS?s Scientific Manuscript database

Saturated soil column experiments were conducted to investigate the transport, retention, and release behavior of a low concentration (1 mg L-1) of functionalized 14C-labeled multi-walled carbon nanotubes (MWCNTs) in a natural soil under various solution chemistries. Breakthrough curves (BTCs) for M...

Variations in the Peak Position of the 6.2 micron Interstellar Emission Feature: A Tracer of N in the Interstellar Polycyclic Aromatic Hydrocarbon Population

NASA Technical Reports Server (NTRS)

Hudgins, Douglas M.; Bauschlicher, Charles W.; Allamandola, L. J.

2005-01-01

This paper presents the results of an investigation of the molecular characteristics that underlie the observed peak position and profile of the nominal 6.2 micron interstellar emission band generally attributed to the CC stretching vibrations of polycyclic aromatic hydrocarbons (PAHs). It begins with a summary of recent experimental and theoretical studies ofthe spectroscopic properties of large (>30 carbon atoms) PAH cations as they relate to this aspect of the astrophysical problem. It then continues with an examination of the spectroscopic properties of a number of PAH variants within the context of the interstellar 6.2 micron emission, beginning with a class of compounds known as polycyclic aromatic nitrogen heterocycles (PANHs; PAHs with one or more nitrogen atoms substituted into their carbon skeleton). In this regard, we summarize the results of recent relevant experimental studies involving a limited set of small PANHs and their cations and then report the results of a comprehensive computational study that extends that work to larger PANH cations including many nitrogen-substituted variants of coronene(+) (C24H12(+)), ovalene(+) (C32H14(+)), circumcoronene(+) (C54H18(+)), and circum-circumcoronene(+) (C96H24(+)). Finally, we report the results of more focused computational studies of selected representatives from a number of other classes of PAH variants that share one or more of the key attributes of the PANH species studied. These alternative classes of PAH variants include (1) oxygen- and silicon-substituted PAH cations; (2) PAH-metal ion complexes (metallocenes) involving the cosmically abundant elements magnesium and iron; and (3) large, asymmetric PAH cations. Overall, the studies reported here demonstrate that increasing PAH size alone is insuEcient to account for the position of the shortest wavelength interstellar 6.2 micron emission bands, as had been suggested by earlier studies. On the other hand, this work reveals that substitution of one or more nitrogen atoms within the interior of the carbon skeleton of a PAH cation induces a significant blueshift in the position of the dominant CC stretching feature of these compounds that is suf6cient to account for the position of the interstellar bands. Subsequent studies of the effects of substitution by other heteroatoms (O and Si), metal ion complexation (Fe(+), Mg(+), and Mg(2+)), and molecular symmetry variation-all of which fail to reproduce the blueshift observed in the PANH cations-indicate that N appears to be unique in its ability to accommodate the position of the interstellar 6.2 micron bands while simultaneously satisfying the other constraints of the astrophysical problem. This result implies that the peak position of the interstellar feature near 6.2 micron traces the degree of nitrogen substitution in the population, that most of the PAHs responsible for the interstellar IR emission features incorporate nitrogen within their aromatic networks, and that a lower limit of 1%-2% of the cosmic nitrogen is sequestered within the interstellar PAH population. Finally, in view of the ubiquity and abundance of interstellar PAHs and the permanent dipoles and distinctive electronic structures of these nitrogen-substituted variants, this work impacts a wide range of observational phenomena outside of the infrared region of the spectrum including the forest of unidentified molecular rotational features and the anomalous Galactic foreground emission in the microwave, and the diffuse interstellar bands (DIBs) and other structure in the interstellar extinction curve in the ulhviolet/visible. These astrophysical ramifications are discussed, and the dipole moments and rotational constants are tabulated to facilitate further investigations of the astrophysical role of nitrogen-substituted aromatic compounds.

l-Tryptophan Radical Cation Electron Spin Resonance Studies: Connecting Solution-derived Hyperfine Coupling Constants with Protein Spectral Interpretations

PubMed Central

Connor, Henry D.; Sturgeon, Bradley E.; Mottley, Carolyn; Sipe, Herbert J.; Mason, Ronald P.

2009-01-01

Fast-flow electron spin resonance (ESR) spectroscopy has been used to detect a free radical formed from the reaction of l-tryptophan with Ce4+ in an acidic aqueous environment. Computer simulations of the ESR spectra from l-tryptophan and several isotopically modified forms strongly support the conclusion that the l-tryptophan radical cation has been detected by ESR for the first time. The hyperfine coupling constants (HFCs) determined from the well-resolved isotropic ESR spectra support experimental and computational efforts to understand l-tryptophan's role in protein catalysis of oxidation-reduction processes. l-tryptophan HFCs facilitated the simulation of fast-flow ESR spectra of free radicals from two related compounds, tryptamine and 3-methylindole. Analysis of these three compounds' β-methylene hydrogen HFC data along with equivalent l-tyrosine data has led to a new computational method that can distinguish between these two amino acid free radicals in proteins without dependence on isotope labeling, electron nuclear double resonance or high-field ESR. This approach also produces geometric parameters (dihedral angles for the β-methylene hydrogens) which should facilitate protein site assignment of observed l-tryptophan radicals as has been done for l-tyrosine radicals. PMID:18433127

Clinical utility for diffusion MRI sequence in emergency and inpatient spine protocols.

PubMed

Hoch, Michael J; Rispoli, Joanne; Bruno, Mary; Wauchope, Mervin; Lui, Yvonne W; Shepherd, Timothy M

Diffusion imaging of the spine has the potential to change clinical management, but is challenging due to the small size of the cord and susceptibility artifacts from adjacent structures. Reduced field-of-view (rFOV) diffusion can improve image quality by decreasing the echo train length. Over the past 2 years, we have acquired a rFOV diffusion sequence for MRI spine protocols on most inpatients and emergency room patients. We provide selected imaging diagnoses to illustrate the utility of including diffusion spine MRI in clinical practice. Our experiences support using diffusion MRI to improve diagnostic certainty and facilitate prompt treatment or clinical management. Copyright © 2017 Elsevier Inc. All rights reserved.

Scandium induced structural transformation and B′:B″ cationic ordering in Pb(Fe{sub 0.5}Nb{sub 0.5})O{sub 3} multiferroic ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mallesham, B.; Ranjith, R., E-mail: ranjith@iith.ac.in; Manivelraja, M.

2014-07-21

The current study explores non-magnetic Sc{sup 3+} induced structural transformation, evolution of local B-site cation ordering and associated effect on ferroelectric phase transition temperature T{sub max} (temperature corresponding to dielectric maxima) on increasing the atom percent of Sc substitution in [Pb(Fe{sub 0.5}Nb{sub 0.5})O{sub 3} (PFN)] ceramics. In this regard, the phase pure Pb[(Fe{sub 0.5−x}Sc{sub x})Nb{sub 0.5}]O{sub 3} ceramics with x varying from 0 to 0.5 were synthesized through solid state reaction route. The detailed structural analysis through Rietveld refinement confirms the room temperature transformation from a monoclinic Cm to rhombohedral R3m structure at x = 0.3 mol. % of Sc. Absorption spectra studies showmore » that there is a considerable increment in the bandgap at higher scandium content. Most interestingly, the T{sub max} exhibited an increment for lower scandium contents (x = 0.1 to 0.25) followed by a drop in T{sub max} (x = 0.3 to 0.5). Such anomalous behavior in T{sub max} is expected to arise due to the onset of B′, B″ local cation ordering beyond Sc content x = 0.25. The B-site cation ordering at and beyond x = 0.3 was also confirmed by the evolution of cation order induced Pb-O coupled vibrational mode in Raman scattering studies. In addition, the Mössbauer spectra of PFN (x = 0) and Pb(Fe{sub 0.4}Sc{sub 0.1}Nb{sub 0.5})O{sub 3} (x = 0.1) are reported to verify the spin state and oxidation state of iron. The lattice distortion due to the radius ratio difference between a Sc{sup 3+} cation and Fe{sup 3+} cation in low spin state is responsible for the structural transformation, which in turn facilitates a B′:B″ cation ordering.« less

Optimal multi-community network modularity for information diffusion

NASA Astrophysics Data System (ADS)

Wu, Jiaocan; Du, Ruping; Zheng, Yingying; Liu, Dong

2016-02-01

Studies demonstrate that community structure plays an important role in information spreading recently. In this paper, we investigate the impact of multi-community structure on information diffusion with linear threshold model. We utilize extended GN network that contains four communities and analyze dynamic behaviors of information that spreads on it. And we discover the optimal multi-community network modularity for information diffusion based on the social reinforcement. Results show that, within the appropriate range, multi-community structure will facilitate information diffusion instead of hindering it, which accords with the results derived from two-community network.

Grounding electrode and method of reducing the electrical resistance of soils

DOEpatents

Koehmstedt, Paul L.

1980-01-01

A first solution of an electrolyte is injected underground into a volume of soil having negative surface charges on its particles. A cationic surfactant suspended in this solution neutralizes these surface charges of the soil particles within the volume. Following the first solution, a cationic asphalt emulsion suspended in a second solution is injected into the volume. The asphalt emulsion diffuses through the volume and electrostatically bonds with additional soil surrounding the volume such that an electrically conductive water repellant shell enclosing the volume is formed. This shell prevents the leaching of electrolyte from the volume into the additional soil. The second solution also contains a dissolved deliquescent salt which draws water into the volume prior to the formation of the shell. When electrically connected to an electrical installation such as a power line tower, the volume constitutes a grounding electrode for the tower.

Quantum chemistry and excited states: First investigations on pyrene-like molecules

NASA Technical Reports Server (NTRS)

Parisel, Olivier; Ellinger, Y.

1994-01-01

Although the calculations are expected to be accurate within 10%, it follows then that there cannot be proposed unquestionable one-to-one attribution due to the density of the DIB's (Diffuse Interstellar Bands). Nevertheless, it has been shown that if one is interested in the experimental study of methyl-pyrene cations, for example, then, the most promising candidate is the 1-methyl isomer: this isomer has been investigated by d'Hendecourt and Leger (1993,1994) and their spectrum shows very striking features in very good agreement with both our calculations and a few DIB's. However, 1-methyl-pyrene cation is not the only product susceptible of being formed in this experiment, and further investigations are in progress to give a complete interpretations of the results. This preliminary report on pyrene-like molecules illustrates the role that theoretical calculations can ply in both the design and the interpretation of experiments.

A simulation study of CS2 solutions in two related ionic liquids with dications and monocations

NASA Astrophysics Data System (ADS)

Lynden-Bell, R. M.; Quitevis, E. L.

2018-05-01

Atomistic simulations of solutions of CS2 in an ionic liquid, [C8(C1im)2 ] [NTf2]2, with a divalent cation and in the corresponding ionic liquid with a monovalent cation, [C4C1im][NTf2], were carried out. The low-frequency librational density of states of the CS2 was of particular interest in view of recent optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). Compared to the monocation ionic liquid, the maximum shifts to higher frequencies in the dication ionic liquid under ambient conditions, but was found to be significantly pressure-dependent. CS2 molecules lie above and below the plane of the imidazolium rings and found to be close to the butyl tails of the monocation. The diffusion rates and embedding energies of solvent ions and CS2 in the two ionic liquids were measured.

Adsorption of anionic and cationic dyes on activated carbon from aqueous solutions: equilibrium and kinetics.

PubMed

Rodríguez, Araceli; García, Juan; Ovejero, Gabriel; Mestanza, María

2009-12-30

Activated carbon was utilized as adsorbent to remove anionic dye, Orange II (OII), and cationic dye, Methylene blue (MB), from aqueous solutions by adsorption. Batch experiments were conducted to study the effects of temperature (30-65 degrees C), initial concentration of adsorbate (300-500 mg L(-1)) and pH (3.0-9.0) on dyes adsorption. Equilibrium adsorption isotherms and kinetics were investigated. The equilibrium experimental data were analyzed by the Langmuir, Freundlich, Toth and Redlich-Peterson models. The kinetic data obtained with different carbon mass were analyzed using a pseudo-first order, pseudo-second order, intraparticle diffusion, Bangham and Chien-Clayton equations. The best results were achieved with the Langmuir isotherm equilibrium model and with the pseudo-second order kinetic model. The activated carbon was found to be very effective as adsorbent for MB and OII from aqueous solutions.

Targeted drug delivery across the blood brain barrier in Alzheimer's disease.

PubMed

Rocha, Sandra

2013-01-01

The discovery of drugs for Alzheimer's disease (AD) therapy that can also permeate the blood brain barrier (BBB) is very difficult owing to its specificity and restrictive nature. The BBB disruption or the administration of the drug directly into the brain is not an option due to toxic effects and low diffusion of the therapeutic molecule in the brain parenchyma. A promising approach for drug systemic delivery to the central nervous system is the use of nanosized carriers. The therapeutic potential of certain nanopharmaceuticals for AD has already been demonstrated in vivo after systemic delivery. They are based on i) conjugates of drug and monoclonal antibodies against BBB endogenous receptors; ii) cationized or end terminal protected proteins/peptides; iii) liposomes and polymeric nanoparticles coated with polysorbate 80, cationic macromolecules or antibodies against BBB receptors/amyloid beta-peptides. Optimization and further validation of these systems are needed.

Interactions between water and 1-butyl-1-methylpyrrolidinium ionic liquids

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fadeeva, Tatiana A.; DeVine, Jessalyn A.; Castner, Edward W., E-mail: ed.castner@rutgers.edu

2015-08-14

We report experimental results on the diffusivity of water in two ionic liquids obtained using the pulsed-gradient spin-echo NMR method. Both ionic liquids have the same cation, 1-butyl-1-methylpyrrolidinium, but different trifluoromethyl-containing anions. One has a strongly hydrophobic anion, bis(trifluoromethylsulfonyl)amide, while the second has a hydrophilic anion, trifluoromethylsulfonate. Transport of water in these ionic liquids is much faster than would be predicted from hydrodynamic laws, indicating that the neutral water molecules experience a very different friction than the anions and cations at the molecular level. Temperature-dependent viscosities, conductivities, and densities are reported as a function of water concentration to further analyzemore » the properties of the ionic liquid-water mixtures. These results on the properties of water in ionic liquids should be of interest to researchers in diverse areas ranging from separations, solubilizing biomass and energy technologies.« less

Descriptors for ions and ion-pairs for use in linear free energy relationships.

PubMed

Abraham, Michael H; Acree, William E

2016-01-22

The determination of Abraham descriptors for single ions is reviewed, and equations are given for the partition of single ions from water to a number of solvents. These ions include permanent anions and cations and ionic species such as carboxylic acid anions, phenoxide anions and protonated base cations. Descriptors for a large number of ions and ionic species are listed, and equations for the prediction of Abraham descriptors for ionic species are given. The application of descriptors for ions and ionic species to physicochemical processes is given; these are to water-solvent partitions, HPLC retention data, immobilised artificial membranes, the Finkelstein reaction and diffusion in water. Applications to biological processes include brain permeation, microsomal degradation of drugs, skin permeation and human intestinal absorption. The review concludes with a section on the determination of descriptors for ion-pairs. Copyright © 2015 Elsevier B.V. All rights reserved.

Synthesis, structures and properties of three copper complexes with dibutyldithiocarbamate ligand

NASA Astrophysics Data System (ADS)

Wang, Chen; Niu, Jiao; Li, Jun; Ma, Xiaoxun

2017-05-01

Three copper complexes constructed with sulfur-containing dibutyldithiocarbamate ligand (DDTC), [(Et2NCS2)4Cu2] (1), [(Et2NCS2)(EtO)Cu]2 (2) and [(Et2NCS2)6Cu13I10]n (3) have been synthesized through the reaction of CuI with different mole ratios of DDTC under solution-diffusion conditions. The single crystal X-ray diffraction revealed that divalent Cu cations in complexes 1 and 2 imply that the reactant, Cu(I), was involved in the redox process. They formed binuclear complexes according to bridging S from DDTC ligands and O atoms from ethanol molecules respectively. The mixed valence Cu cations had two types of coordination environments in complex 3 and formed a two-dimensional layered coordination polymer by bridging the five-core Cu(I) clusters and Cu(II). The powder X-ray diffraction, luminescent, thermogravimetric analysis, etc. were also studied in this paper.

Diffuse noxious inhibitory controls and nerve injury: restoring an imbalance between descending monoamine inhibitions and facilitations.

PubMed

Bannister, Kirsty; Patel, Ryan; Goncalves, Leonor; Townson, Louisa; Dickenson, Anthony H

2015-09-01

Diffuse noxious inhibitory controls (DNICs) utilize descending inhibitory controls through poorly understood brain stem pathways. The human counterpart, conditioned pain modulation, is reduced in patients with neuropathy aligned with animal data showing a loss of descending inhibitory noradrenaline controls together with a gain of 5-HT3 receptor-mediated facilitations after neuropathy. We investigated the pharmacological basis of DNIC and whether it can be restored after neuropathy. Deep dorsal horn neurons were activated by von Frey filaments applied to the hind paw, and DNIC was induced by a pinch applied to the ear in isoflurane-anaesthetized animals. Spinal nerve ligation was the model of neuropathy. Diffuse noxious inhibitory control was present in control rats but abolished after neuropathy. α2 adrenoceptor mechanisms underlie DNIC because the antagonists, yohimbine and atipamezole, markedly attenuated this descending inhibition. We restored DNIC in spinal nerve ligated animals by blocking 5-HT3 descending facilitations with the antagonist ondansetron or by enhancing norepinephrine modulation through the use of reboxetine (a norepinephrine reuptake inhibitor, NRI) or tapentadol (μ-opioid receptor agonist and NRI). Additionally, ondansetron enhanced DNIC in normal animals. Diffuse noxious inhibitory controls are reduced after peripheral nerve injury illustrating the central impact of neuropathy, leading to an imbalance in descending excitations and inhibitions. Underlying noradrenergic mechanisms explain the relationship between conditioned pain modulation and the use of tapentadol and duloxetine (a serotonin, NRI) in patients. We suggest that pharmacological strategies through manipulation of the monoamine system could be used to enhance DNIC in patients by blocking descending facilitations with ondansetron or enhancing norepinephrine inhibitions, so possibly reducing chronic pain.

Transport of salicylic acid through monolayers of a kidney epithelial cell line (LLC-PK1).

PubMed

Chatton, J Y; Roch-Ramel, F

1992-05-01

LLC-PK1 cells were used as a model of renal proximal epithelium to study the nonionic diffusion of salicylic acid (SAL). The apparent [14C]SAL transcellular permeability (PSal) and intracellular content were estimated at 20-21 degrees C from fluxes measured across cell monolayers grown on filters, in both apical-to-basolateral and basolateral-to-apical directions. The medium pH of the cis-side was varied from 6.0 to 7.4, and the medium pH of the trans-side was kept at 7.4. In the apical-to-basolateral direction, PSal increased linearly with the calculated concentration of nonionized SAL, indicating that SAL permeability was essentially the result of nonionic diffusion. In the basolateral-to-apical direction, PSal was about 2.5-fold higher than in the apical-to-basolateral direction and was not linearly related to the concentration of nonionized SAL molecules (0-4.5 nM), suggesting that besides nonionic diffusion, SAL was transported in its ionized form by a facilitated mechanism still active at 21 degrees C. This was confirmed by measuring basolateral-to-apical fluxes at 37 degrees C and observing that probenecid, an inhibitor of organic anion secretion, and cold SAL decreased PSal. Interestingly, at 37 degrees C, PSal in the apical-to-basolateral direction was also decreased by probenecid and cold SAL, suggesting the existence of a facilitated transport in this direction. These data demonstrated that the secretory transport of SAL is present in LLC-PK1 cells. The facilitated transport observed in the apical-to-basolateral direction suggests that in proximal tubule, SAL reabsorption might occur by facilitated mechanism and nonionic diffusion.

Viscosity, conductivity, and electrochemical property of dicyanamide ionic liquids

NASA Astrophysics Data System (ADS)

Yuan, Wen-Li; Yang, Xiao; He, Ling; Xue, Ying; Qin, Song; Tao, Guo-Hong

2018-03-01

The instructive structure-property relationships of ionic liquids (ILs) can be put to task-specific design of new functionalized ILs. The dicyanamide (DCA) ILs are typical CHN type ILs which are halogen free, chemical stable, low-viscous and fuel-rich. The transport properties of DCA ionic liquids are significant for their applications as solvents, electrolytes and hypergolic propellants. This work systematically investigates several important transport properties of four DCA ILs ([C4mim][N(CN)2], [C4m2im][N(CN)2], N4442[N(CN)2], and N8444[N(CN)2]) including viscosity, conductivity, and electrochemical property at different temperatures. The melting points, temperature-dependent viscosities and conductivities reveal the structure-activity relationship of four DCA ILs. From the Walden plots, the imidazolium cations exhibit stronger cation–anion attraction than the ammonium cations. DCA ILs have relatively high values of electrochemical windows (EWs), which indicates that the DCA ILs are potential candidates for electrolytes in electrochemical applications. The cyclic voltammograms of Eu(III) in these DCA ILs at GC working electrode at various temperatures 303–333 K consists of quasi-reversible waves. The electrochemical properties of the DCA ILs are also dominated by the cationic structures. The current intensity (ip), the diffusion coefficients (Do), the charge transfer rate constants (ks) of Eu(III) in DCA ILs all increased with the molar conductivities increased. The cationic structure-transport property relationships of DCA ILs were constructed for designing novel functionalized ILs to fulfill specific demands.

Claudin-2-mediated cation and water transport share a common pore

PubMed Central

Rosenthal, Rita; Günzel, Dorothee; Krug, Susanne M.; Schulzke, Jörg-Dieter; Fromm, Michael; Yu, Alan S.L.

2016-01-01

Aim Claudin-2 is a tight junction protein typically located in “leaky” epithelia exhibiting large paracellular permeabilities like small intestine and proximal kidney tubule. Former studies revealed that claudin-2 forms paracellular channels for small cations like sodium and potassium and also paracellular channels for water. This study analyzes whether the diffusive transport of sodium and water occurs through a common pore of the claudin-2 channel. Methods Wild-type claudin-2 and different claudin-2 mutants were expressed in MDCK I kidney tubule cells using an inducible system. Ion and water permeability and the effect of blocking reagents on both were investigated on different clones of the mutants. Results Neutralization of a negatively charged cation interaction site in the pore with the mutation, D65N, decreased both, sodium permeability and water permeability. Claudin-2 mutants (I66C and S68C) with substitution of the pore-lining amino acids with cysteine were used to test the effect of steric blocking of the claudin-2 pore by thiol-reactive reagents. Addition of thiol-reactive reagents to these mutants simultaneously decreased conductance and water permeability. Remarkably, all experimental perturbations caused parallel changes in ion conductance and water permeability, disproving different or independent passage pathways. Conclusion Our results indicate that claudin-2-mediated cation and water transport are frictionally coupled and share a common pore. This pore is lined and determined in permeability by amino acid residues of the first extracellular loop of claudin-2. PMID:27359349

Viscosity, Conductivity, and Electrochemical Property of Dicyanamide Ionic Liquids

PubMed Central

Yuan, Wen-Li; Yang, Xiao; He, Ling; Xue, Ying; Qin, Song; Tao, Guo-Hong

2018-01-01

The instructive structure-property relationships of ionic liquids (ILs) can be put to task-specific design of new functionalized ILs. The dicyanamide (DCA) ILs are typical CHN type ILs which are halogen free, chemical stable, low-viscous, and fuel-rich. The transport properties of DCA ionic liquids are significant for their applications as solvents, electrolytes, and hypergolic propellants. This work systematically investigates several important transport properties of four DCA ILs ([C4mim][N(CN)2], [C4m2im][N(CN)2], N4442[N(CN)2], and N8444[N(CN)2]) including viscosity, conductivity, and electrochemical property at different temperatures. The melting points, temperature-dependent viscosities and conductivities reveal the structure-activity relationship of four DCA ILs. From the Walden plots, the imidazolium cations exhibit stronger cation–anion attraction than the ammonium cations. DCA ILs have relatively high values of electrochemical windows (EWs), which indicates that the DCA ILs are potential candidates for electrolytes in electrochemical applications. The cyclic voltammograms of Eu(III) in these DCA ILs at GC working electrode at various temperatures 303–333 K consists of quasi-reversible waves. The electrochemical properties of the DCA ILs are also dominated by the cationic structures. The current intensity (ip), the diffusion coefficients (Do), the charge transfer rate constants (ks) of Eu(III) in DCA ILs all increased with the molar conductivities increased. The cationic structure-transport property relationships of DCA ILs were constructed for designing novel functionalized ILs to fulfill specific demands. PMID:29600245

Effect of Ion Rigidity on Physical Properties of Ionic Liquids Studied by Molecular Dynamics Simulation.

PubMed

Ramírez-González, Pedro E; Ren, Gan; Saielli, Giacomo; Wang, Yanting

2016-06-30

In this work, we have performed molecular dynamics (MD) simulations to compare the structural and dynamical properties of three ionic liquids (ILs), 1-ethyl-3-methyl-imidazolium tetrafluorborate ([EMI(+)][BF4(-)]), 1,1'-dimethyl-4,4'-bipyridinium bis(tetrafluorborate) ([VIO(2+)][BF4(-)]2), and 1,1'-dimethyl-4,4'-bipyridinium bis(trifluoromethylsulfonyl)imide (bistriflimide in short) ([VIO(2+)][Tf2N(-)]2), aiming to discover the influence of ion rigidity on the physical properties of ILs. [VIO(2+)] is more rigid than [EMI(+)], and [BF4(-)] is more rigid than [Tf2N(-)]. [VIO(2+)][BF4(-)]2 has an anion distribution different from the other two by the higher and sharper peaks in the cation-anion radial distribution functions, reflecting a close-packed local structure of anions around cations. [VIO(2+)][BF4(-)]2 and [VIO(2+)][Tf2N(-)]2 have similar dynamics much slower than [EMI(+)][BF4(-)], and [VIO(2+)][Tf2N(-)]2 shows a more isotropic molecular distribution than [VIO(2+)][BF4(-)]2 and [EMI(+)][BF4(-)]. Additionally, we have simulated two modified viologen-based ILs to reinforce our interpretations. We conclude from the above simulation results that the rigidity of anions influences the alignment of cations and that the rigidity of cations shows a large obstacle to their rotational capacity. Moreover, we have observed a slower diffusion of [VIO(2+)][BF4(-)]2 due to the electrostatic correlations, which stabilizes the ion-cage effect.

Enhancing thermoelectrochemical properties by tethering ferrocene to the anion or cation of ionic liquids: altered thermodynamics and solubility.

PubMed

Aldous, Leigh; Black, Jeffrey J; Elias, Maximo C; Gélinas, Bruno; Rochefort, Dominic

2017-09-13

Entropic changes inherent within a redox process typically result in significant temperature sensitivity. This can be utilised positively or can be a detrimental process. This study has investigated the thermoelectrochemical properties (temperature-dependant electrochemistry) of the ferrocenium|ferrocene redox couple in an ionic liquid, and in particular the effect of covalently tethering this redox couple to fixed positive or negative charges. As such, the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide was employed to dissolve ferrocene, as well as cationic-tethered ferrocene (the 1-ethyl-3-(methylferrocenyl)imidazolium cation) and anionic-tethered ferrocene (the ferrocenylsulfonyl(trifluoromethylsulfonyl)imide anion). These systems were characterised in terms of their voltammetry (apparent formal potentials, diffusion coefficients and electron transfer rate constants) and thermoelectrochemistry (temperature coefficients of the cell potential or 'Seebeck coefficients', short circuit current densities and power density outputs). The oxidised cationic species behaved like a dicationic species and was thus 6-fold more effective at converting waste thermal energy to electrical power within a thermoelectrochemical cell than unmodified ferrocene. This was almost exclusively due to a significant boost in the Seebeck coefficient of this redox couple. Conversely, the oxidised anionic species was formally a zwitterion, but this zwitterionic species behaved thermodynamically like a neutral species. The inverted entropic change upon going from ferrocene to anion-tethered ferrocene allowed development of a largely temperature-insensitive reference potential based upon a mixture of acetylferrocene and ferricenyl(iii)sulfonyl(trifluoromethylsulfonyl)imide.

Optical (diffuse reflectance) and Mossbauer spectroscopic study of nontronite and related Fe-bearing smectites

USGS Publications Warehouse

Sherman, David M.; Vergo, N.

1988-01-01

Near-ultraviolet to near-infrared optical (diffuse reflectance) spectra of several nontronites and related Fe-bearing smectites [(Fe2+,Fe3+)-bearing saponite and (Fe2+,Fe3+)-bearing montmorillonite] are presented and interpreted. Mossbauer spectra at 298 K are also presented to help interpret the optical spectra. The optical spectra of nontronites are dominated by the ligand field transitions of Fe3+ in octahedral coordination sites. In addition to the ligand field transitions of single Fe3+ cations, a broad absorption band centered near 22000 cm-1 is observed that may be due to the simultaneous excitation of two Fe3+ cations to the 4T1g (4G) state. Alternatively, this band may represent excitations to the 2A2g and 2T1g ligand field states. For most samples, the amount of tetrahedrally coordinated Fe3+ was below that detectable by Mossbauer spectroscopy (1-3% of total Fe). However, the optical spectra of all of the nontronites show an absorption band near 23000 cm-1. This band is assigned to the 6A1 ??? 4E,4A1 transition of tetrahedrally coordinated Fe3+. The optical spectra of mixed-valence Fe-bearing smectites show a broad absorption band at 14000-15000 cm-1 owing to Fe2+ ??? Fe3+ charge transfer. -from Authors

Use of polyurethane foam and 3-hydroxy-7,8-benzo-1,2,3,4-tetrahydroquinoline for determination of nitrite by diffuse reflectance spectroscopy and colorimetry.

PubMed

Apyari, V V; Dmitrienko, S G; Ostrovskaya, V M; Anaev, E K; Zolotov, Y A

2008-07-01

Polyurethane foam (PUF) has been suggested as a solid polymeric reagent for determination of nitrite. The determination is based on the diazotization of end toluidine groups of PUF with nitrite in acidic medium followed by coupling of polymeric diazonium cation with 3-hydroxy-7,8-benzo-1,2,3,4-tetrahydroquinoline. The intensely colored polymeric azodye formed in this reaction can be used as a convenient analytic form for the determination of nitrite by diffuse reflectance spectroscopy (c (min) = 0.7 ng mL(-1)). The possibility of using a desktop scanner, digital camera, and computer data processing for the numerical evaluation of the color intensity of the polymeric azodye has been investigated. A scanner and digital camera can be used for determination of nitrite with the same sensitivity and reproducibility as with diffuse reflectance spectroscopy. The approach developed was applied for determination of nitrite in river water and human exhaled breath condensate.

Atomistic modeling of La3+ doping segregation effect on nanocrystalline yttria-stabilized zirconia.

PubMed

Zhang, Shenli; Sha, Haoyan; Castro, Ricardo H R; Faller, Roland

2018-05-16

The effect of La3+ doping on the structure and ionic conductivity change in nanocrystalline yttria-stabilized zirconia (YSZ) was studied using a combination of Monte Carlo and molecular dynamics simulations. The simulation revealed the segregation of La3+ at eight tilt grain boundary (GB) structures and predicted an average grain boundary (GB) energy decrease of 0.25 J m-2, which is close to the experimental values reported in the literature. Cation stabilization was found to be the main reason for the GB energy decrease, and energy fluctuations near the grain boundary are smoothed out with La3+ segregation. Both dynamic and energetic analysis on the Σ13(510)/[001] GB structure revealed La3+ doping hinders O2- diffusion in the GB region, where the diffusion coefficient monotonically decreases with increasing La3+ doping concentration. The effect was attributed to the increase in the site-dependent migration barriers for O2- hopping caused by segregated La3+, which also leads to anisotropic diffusion at the GB.

Structure and electrostatic property of cytoplasmic domain of ZntB transporter

PubMed Central

Tan, Kemin; Sather, Alicia; Robertson, Janice L; Moy, Shiu; Roux, Benoît; Joachimiak, Andrzej

2009-01-01

ZntB is the distant homolog of CorA Mg2+ transporter within the metal ion transporter superfamily. It was early reported that the ZntB from Salmonella typhimurium facilitated efflux of Zn2+ and Cd2+, but not Mg2+. Here, we report the 1.90 Å crystal structure of the intracellular domain of ZntB from Vibrio parahemolyticus. The domain forms a funnel-shaped homopentamer that is similar to the full-length CorA from Thermatoga maritima, but differs from two previously reported dimeric structures of truncated CorA intracellular domains. However, no Zn2+ or Cd2+ binding sites were identified in the high-resolution structure. Instead, 25 well-defined Cl− ions were observed and some of these binding sites are highly conserved within the ZntB family. Continuum electrostatics calculations suggest that the central pore of the funnel is highly attractive for cations, especially divalents. The presence of the bound Cl− ions increases the stability of cations along the pore suggesting they could be important in enhancing cation transport. PMID:19653298

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tan, K.; Sather, A.; Robertson, J. L.

ZntB is the distant homolog of CorA Mg{sup 2+} transporter within the metal ion transporter superfamily. It was early reported that the ZntB from Salmonella typhimurium facilitated efflux of Zn{sup 2+} and Cd{sup 2+}, but not Mg{sup 2+}. Here, we report the 1.90 {angstrom} crystal structure of the intracellular domain of ZntB from Vibrio parahemolyticus. The domain forms a funnel-shaped homopentamer that is similar to the full-length CorA from Thermatoga maritima, but differs from two previously reported dimeric structures of truncated CorA intracellular domains. However, no Zn{sup 2+} or Cd{sup 2+} binding sites were identified in the high-resolution structure. Instead,more » 25 well-defined Cl{sup -} ions were observed and some of these binding sites are highly conserved within the ZntB family. Continuum electrostatics calculations suggest that the central pore of the funnel is highly attractive for cations, especially divalents. The presence of the bound Cl{sup -} ions increases the stability of cations along the pore suggesting they could be important in enhancing cation transport.« less

Sorption mechanism of enrofloxacin on humic acids extracted from Brazilian soils.

PubMed

Martínez-Mejía, Mónica J; Sato, Isabela; Rath, Susanne

2017-07-01

Veterinary antimicrobials are emerging environmental contaminants of concern. In this study, the sorption of enrofloxacin (ENR) onto humic acids (HAs) extracted from three Brazilian soils was evaluated. HAs were characterized by elemental analysis and solid 13 C nuclear magnetic resonance spectroscopy. The sorption of ENR onto HAs was at least 20-fold higher than onto the soils from which they were separated. Ionic and cation bridging are the primary interactions involved. The interactions driven by cation exchange are predominant on HAs, which appear to have abundant carboxylic groups and a relatively high proportion of H-bond donor moieties with carbohydrate-like structures. Interactions explained by cation bridging and/or surface complexation on HAs are facilitated by moieties containing conjugated ligands, significant content of oxygen-containing functional groups, such as phenolic-OH or lignin-like structures. HAs containing electron-donating phenolic moieties and carboxylic acid ligand groups exhibit a sorption mechanism that is primarily driven by strong metal binding, favoring the formation of ternary complexes between functional groups of the organic matter and drugs.

Ionomers for Ion-Conducting Energy Materials

NASA Astrophysics Data System (ADS)

Colby, Ralph

For ionic actuators and battery separators, it is vital to utilize single-ion conducting ionomers that avoid the detrimental polarization of other ions. Single-ion conducting ionomers are synthesized based on DFT calculations, with low glass transition temperatures (facile dynamics) to prepare ion-conducting membranes for battery separators that conduct Li+ or Na+. Characterization by X-ray scattering, dielectric spectroscopy, FTIR, NMR and linear viscoelasticity collectively develop a coherent picture of ionic aggregation and both counterion and polymer dynamics. 7Li NMR diffusion measurements find that diffusion is faster than expected by conductivity using the Nernst-Einstein equation, which means that the majority of Li diffusion occurs by ion pairs moving with the polymer segmental motion. Segmental motion only contributes to ionic conduction in the rare event that one of these ion pairs has an extra Li (a positive triple ion). This leads us to a new metric for ion-conducting soft materials, the product of the cation number density p0 and their diffusion coefficient D; p0D is the diffusive flux of lithium ions. This new metric has a maximum at intermediate ion content that corresponds to the overlap of ion pair polarizability volumes. At higher ion contents, the ion pairs interact strongly and form larger aggregation states that retard segmental motion of both mobile ion pairs and triple ions.

Radionuclide migration in clayrock host formations for deep geological disposal of radioactive waste: advances in process understanding and up-scaling methods resulting from the EC integrated project `Funmig

NASA Astrophysics Data System (ADS)

Altmann, S.; Tournassat, C.; Goutelard, F.; Parneix, J. C.; Gimmi, T.; Maes, N.

2009-04-01

One of the ‘pillars' supporting Safety Cases for deep geological disposal of radioactive waste in clayrock formations is the knowledge base regarding radionuclide (Rn) retention by sorption and diffusion-driven transport which is why the EC integrated project ‘Funmig' focused a major part of its effort on advancing understanding of these two macroscopic phenomena. This talk presents some of the main results of this four year effort (2005-2008). One of the keys to understanding diffusion-driven transport of anionic and cationic radionuclide species in clayrocks lies in a detailed understanding of the phenomena governing Rn total concentration and speciation (dissolved, adsorbed) in the different types of pore spaces present in highly-compacted masses of permanently charged clay minerals. Work carried out on a specifically synthesized montmorillonite (a model for the clay mineral fraction in clayrocks) led to development, and preliminary experimental validation, of a conceptually coherent set of theoretical models (molecular dynamics, electrostatic double layer, thermodynamic) describing dissolved ion and water solvent behavior in this material. This work, complemented by the existing state of the art, provides a sound theoretical basis for explaining such important phenomena as anion exclusion, cation exchange and the diffusion behavior of anions, weakly sorbing cations and water tracers. Concerning the behavior of strongly sorbing and/or redox-reactive radionuclides in clay systems, project research improved understanding of the nature of sorption reactions and sorbed species structure for key radioelements, or analogues (U, Se, Eu, Sm, Yb, Nd) on the basal surfaces and in the interlayers of synthetic or purified clay minerals. A probable mechanism for Se(IV) retention by reduction to Se° in Fe2+-containing clays was brought to light; this same process was also studied on the Callovo-Oxfordien clayrock targeted by the French radwaste management program. The migration of most radionuclides in clayrocks, in particular the actinides, is limited by their strong sorption on rock mineral surfaces. Much effort was devoted in Funmig to improving understanding of this process on the clayrocks being studied in the Swiss, Belgian and French radwaste management programs. Specific attention was focused on (i) elucidating the effect of dissolved organic matter on Am(III), Th(IV), Eu(III) sorption on clayrock surfaces and (ii) determining the link between Kd measured on dispersed rock systems and the Kd operant in intact rock volumes, i.e. during diffusion. Regarding the latter question, results indicate that Kd values for ‘dispersed' and ‘intact' materials are quite similar for certain elements (Na, Sr, Cs, Co). On the other hand, Kd values obtained by modeling results of diffusion experiments involving strongly sorbing elements as Cs, Co and Eu were always significantly smaller than those predicted based on sorption data measured in corresponding batch systems. This is an area where additional research is being planned. A major effort was devoted to improving understanding of the effects of small-scale (m to cm) clayrock structure and large-scale (dm to hm) mineralogical composition on radionuclide diffusion-retention. The program focusing on the small-scale produced a method for simulating the results of tracer diffusion in an intact rock based on the actual rock microstructure of the rock sample to be used in the diffusion experiment. This model was used to predict / inverse model the spatial distribution of highly sorbing tracers (Eu, Cu). This overall approach is also being used to understand how changes in mineralogical composition can affect the values of macroscopic diffusion parameters (De, tortuosity, anisiotropy). At a much larger scale, the results of (i) a geostatistical analysis of clayrock mineralogical variability and (ii) measurements of De and Kd dependence on mineralogy for Cs and Cl, were combined to create models of parameter variability at the formation scale. These models were used to evaluate the effects of formation scale heterogeneity on predictive modeling of radionuclide migration. Measurements and modeling of natural tracer profiles were also carried out in order to evaluate the diffusion characteristics at geological time and space scales.

An Introduction to Zeolite Synthesis Using Imidazolium-Based Cations as Organic Structure-Directing Agents.

PubMed

Vinaches, Paloma; Bernardo-Gusmão, Katia; Pergher, Sibele B C

2017-08-06

Zeolite synthesis is a wide area of study with increasing popularity. Several general reviews have already been published, but they did not summarize the study of imidazolium species in zeolite synthesis. Imidazolium derivatives are promising compounds in the search for new zeolites and can be used to help understand the structure-directing role. Nearly 50 different imidazolium cations have already been used, resulting in a variety of zeolitic types, but there are still many derivatives to be studied. In this context, the purpose of this short review is to help researchers starting in this area by summarizing the most important concepts related to imidazolium-based zeolite studies and by presenting a table of recent imidazolium derivatives that have been recently studied to facilitate filling in the knowledge gaps.

Regulation of Cation Balance in Saccharomyces cerevisiae

PubMed Central

Cyert, Martha S.; Philpott, Caroline C.

2013-01-01

All living organisms require nutrient minerals for growth and have developed mechanisms to acquire, utilize, and store nutrient minerals effectively. In the aqueous cellular environment, these elements exist as charged ions that, together with protons and hydroxide ions, facilitate biochemical reactions and establish the electrochemical gradients across membranes that drive cellular processes such as transport and ATP synthesis. Metal ions serve as essential enzyme cofactors and perform both structural and signaling roles within cells. However, because these ions can also be toxic, cells have developed sophisticated homeostatic mechanisms to regulate their levels and avoid toxicity. Studies in Saccharomyces cerevisiae have characterized many of the gene products and processes responsible for acquiring, utilizing, storing, and regulating levels of these ions. Findings in this model organism have often allowed the corresponding machinery in humans to be identified and have provided insights into diseases that result from defects in ion homeostasis. This review summarizes our current understanding of how cation balance is achieved and modulated in baker’s yeast. Control of intracellular pH is discussed, as well as uptake, storage, and efflux mechanisms for the alkali metal cations, Na+ and K+, the divalent cations, Ca2+ and Mg2+, and the trace metal ions, Fe2+, Zn2+, Cu2+, and Mn2+. Signal transduction pathways that are regulated by pH and Ca2+ are reviewed, as well as the mechanisms that allow cells to maintain appropriate intracellular cation concentrations when challenged by extreme conditions, i.e., either limited availability or toxic levels in the environment. PMID:23463800

Surface area of montmorillonite from the dynamic sorption of nitrogen and carbon dioxide

USGS Publications Warehouse

Thomas, Josephus; Bohor, Bruce F.

1968-01-01

Surface area determinations were made on a montmorillonite with various cations emplaced on the exchangeable sites, utilizing nitrogen and carbon dioxide as adsorbates at 77°K and 195°K, respectively, in a dynamic system. From the fraction of a Mississippi montmorillonite less than about 1 μ in size, samples were prepared by replacing the original exchangeable cations with Li+, Na+, K+, Rb+, Cs+, Mg++, Ca++, Ba++, and NH4+, forming a series of homoionic montmorillonite species.Surface areas from 3-point B.E.T. plots (half-hour adsorption points), with nitrogen as the adsorbate, ranged from 61 m2/g for Li-montmorillonite to 138 m2/g for Cs-montmorillonite, thus reflecting a certain degree of nitrogen penetration between layers. Complete penetration should theoretically result in a surface area of over 300 m2/g for this clay with a nitrogen monolayer between each pair of platelets. The experimental data indicate that the extent of penetration is time-dependent and is also a function of the interlayer forces as governed by the size and charge of the replaceable cation. This finding negates the generally accepted concept that nitrogen at 77°K does not penetrate the layers and provides a measure only of the external surface of expandable clay minerals.A further measure of the variation of interlayer forces is provided by the adsorption of carbon dioxide at 195°K. Surface area values ranged from 99 m2/g for Li-montmorillonite to 315 m2/g for Csmontmorillonite. Although the carbon dioxide molecule is larger than the nitrogen molecule, its greater penetration apparently is a result of its being kinetically more energetic (with a larger diffusion coefficient) at its higher adsorption temperature. Similar differences have been found with both adsorbates in the study of microporous substances, such as coal, where activated diffusion is of considerable significance.

The helical structure of DNA facilitates binding

NASA Astrophysics Data System (ADS)

Berg, Otto G.; Mahmutovic, Anel; Marklund, Emil; Elf, Johan

2016-09-01

The helical structure of DNA imposes constraints on the rate of diffusion-limited protein binding. Here we solve the reaction-diffusion equations for DNA-like geometries and extend with simulations when necessary. We find that the helical structure can make binding to the DNA more than twice as fast compared to a case where DNA would be reactive only along one side. We also find that this rate advantage remains when the contributions from steric constraints and rotational diffusion of the DNA-binding protein are included. Furthermore, we find that the association rate is insensitive to changes in the steric constraints on the DNA in the helix geometry, while it is much more dependent on the steric constraints on the DNA-binding protein. We conclude that the helical structure of DNA facilitates the nonspecific binding of transcription factors and structural DNA-binding proteins in general.

An Assessment of Social Diffusion in the Respecting Choices Advance Care Planning Program

ERIC Educational Resources Information Center

Moorman, Sara M.; Carr, Deborah; Kirchhoff, Karin T.; Hammes, Bernard J.

2012-01-01

This study examines the potential social diffusion effects of the Respecting Choices advance care planning program administered in La Crosse, Wisconsin, since 1991. The program produces educational materials for patients, trains facilitators to help patients prepare for end of life, and ensures that advance directives are connected to patients'…

A ligand exchange strategy for one-pot sequential synthesis of (hyperbranched polyethylene)-b-(linear polyketone) block polymers.

PubMed

Zhang, Zhichao; Ye, Zhibin

2012-08-18

Upon the addition of an equimolar amount of 2,2'-bipyridine, a cationic Pd-diimine complex capable of facilitating "living" ethylene polymerization is switched to catalyze "living" alternating copolymerization of 4-tertbutylstyrene and CO. This unique chemistry is thus employed to synthesize a range of well-defined treelike (hyperbranched polyethylene)-b-(linear polyketone) block polymers.

Organizational Information Dissemination within Collaborative Networks Using Digital Communication Tools

ERIC Educational Resources Information Center

Hinojosa, Cristelia Zarate

2017-01-01

While knowledge is one of an organization's greatest assets, it remains a challenge to facilitate knowledge transfer between people within an organization. Social influence has been studied in its role of facilitating information diffusion, which is necessary for knowledge transfer to occur. Among this research, tie strength, a quantifiable…

Roles of cation valance and exchange on the retention and colloid-facilitated transport of functionalized multi-walled carbon nanotubes in a natural soil.

PubMed

Zhang, Miaoyue; Bradford, Scott A; Šimůnek, Jirka; Vereecken, Harry; Klumpp, Erwin

2017-02-01

Saturated soil column experiments were conducted to investigate the transport, retention, and release behavior of a low concentration (1 mg L -1 ) of functionalized 14 C-labeled multi-walled carbon nanotubes (MWCNTs) in a natural soil under various solution chemistries. Breakthrough curves (BTCs) for MWCNTS exhibited greater amounts of retardation and retention with increasing solution ionic strength (IS) or in the presence of Ca 2+ in comparison to K + , and retention profiles (RPs) for MWCNTs were hyper-exponential in shape. These BTCs and RPs were well described using the advection-dispersion equation with a term for time- and depth-dependent retention. Fitted values of the retention rate coefficient and the maximum retained concentration of MWCNTs were higher with increasing IS and in the presence of Ca 2+ in comparison to K + . Significant amounts of MWCNT and soil colloid release was observed with a reduction of IS due to expansion of the electrical double layer, especially following cation exchange (when K + displaced Ca 2+ ) that reduced the zeta potential of MWCNTs and the soil. Analysis of MWCNT concentrations in different soil size fractions revealed that >23.6% of the retained MWCNT mass was associated with water-dispersible colloids (WDCs), even though this fraction was only a minor portion of the total soil mass (2.38%). More MWCNTs were retained on the WDC fraction in the presence of Ca 2+ than K + . These findings indicated that some of the released MWCNTs by IS reduction and cation exchange were associated with the released clay fraction, and suggests the potential for facilitated transport of MWCNT by WDCs. Published by Elsevier Ltd.

Remediating munitions-contaminated soil with zerovalent iron and cationic surfactants.

PubMed

Park, J; Comfort, S D; Shea, P J; Machacek, T A

2004-01-01

Soils contaminated from military operations often contain mixtures of HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine), RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine), and TNT (2,4,6-trinitrotoluene) rather than a single explosive. Differences among explosives in solubility and reactivity make developing a single remediation treatment difficult. When Fe(0) was used to treat a munitions-contaminated soil, we observed high rates of destruction for RDX and TNT (98%) but not HMX. Our objective was to determine if HMX destruction by Fe(0) could be enhanced by increasing HMX solubility by physical (temperature) or chemical (surfactants) means. To determine electron acceptor preference, we treated RDX and HMX with Fe(0) in homogeneous solutions and binary mixtures. Increasing aqueous temperature (20 to 55 degrees C) increased HMX solubility (2 to 22 mg L(-1)) but did not increase destruction by Fe(0) in a contaminated soil slurry that also contained RDX and TNT. Batch experiments using equal molar concentrations of RDX and HMX demonstrated that RDX was preferentially reduced over HMX by Fe(0). By testing various surfactants, we found that the cationic surfactants (HDTMA [hexadecyltrimethylammonium bromide], didecyl, and didodecyl) were most effective in increasing HMX concentration in solution. Didecyl and HDTMA were also found to be highly effective in facilitating the transformation of HMX by Fe(0). Using HDTMA or didecyl solutions (3%, w/v) containing solid-phase HMX, we observed that 100% of the added HMX was transformed by Fe(0) in the didecyl matrix and 60% in the HDTMA matrix. These results indicate that cationic surfactants can increase HMX solubility and facilitate Fe(0)-mediated transformation kinetics but HMX destruction rates will be slowed when RDX is present.

Accurate prediction of cation-π interaction energy using substituent effects.

PubMed

Sayyed, Fareed Bhasha; Suresh, Cherumuttathu H

2012-06-14

Substituent effects on cation-π interactions have been quantified using a variety of Φ-X···M(+) complexes where Φ, X, and M(+) are the π-system, substituent, and cation, respectively. The cation-π interaction energy, E(M(+)), showed a strong linear correlation with the molecular electrostatic potential (MESP) based measure of the substituent effect, ΔV(min) (the difference between the MESP minimum (V(min)) on the π-region of a substituted system and the corresponding unsubstituted system). This linear relationship is E(M(+)) = C(M(+))(ΔV(min)) + E(M(+))' where C(M(+)) is the reaction constant and E(M(+))' is the cation-π interaction energy of the unsubstituted complex. This relationship is similar to the Hammett equation and its first term yields the substituent contribution of the cation-π interaction energy. Further, a linear correlation between C(M(+))() and E(M(+))()' has been established, which facilitates the prediction of C(M(+)) for unknown cations. Thus, a prediction of E(M(+)) for any Φ-X···M(+) complex is achieved by knowing the values of E(M(+))' and ΔV(min). The generality of the equation is tested for a variety of cations (Li(+), Na(+), K(+), Mg(+), BeCl(+), MgCl(+), CaCl(+), TiCl(3)(+), CrCl(2)(+), NiCl(+), Cu(+), ZnCl(+), NH(4)(+), CH(3)NH(3)(+), N(CH(3))(4)(+), C(NH(2))(3)(+)), substituents (N(CH(3))(2), NH(2), OCH(3), CH(3), OH, H, SCH(3), SH, CCH, F, Cl, COOH, CHO, CF(3), CN, NO(2)), and a large number of π-systems. The tested systems also include multiple substituted π-systems, viz. ethylene, acetylene, hexa-1,3,5-triene, benzene, naphthalene, indole, pyrrole, phenylalanine, tryptophan, tyrosine, azulene, pyrene, [6]-cyclacene, and corannulene and found that E(M)(+) follows the additivity of substituent effects. Further, the substituent effects on cationic sandwich complexes of the type C(6)H(6)···M(+)···C(6)H(5)X have been assessed and found that E(M(+)) can be predicted with 97.7% accuracy using the values of E(M(+))' and ΔV(min). All the Φ-X···M(+) systems showed good agreement between the calculated and predicted E(M(+))() values, suggesting that the ΔV(min) approach to substituent effect is accurate and useful for predicting the interactive behavior of substituted π-systems with cations.

Uptake of L-nicotine and of 6-hydroxy-L-nicotine by Arthrobacter nicotinovorans and by Escherichia coli is mediated by facilitated diffusion and not by passive diffusion or active transport.

PubMed

Ganas, Petra; Brandsch, Roderich

2009-06-01

The mechanism by which l-nicotine is taken up by bacteria that are able to grow on it is unknown. Nicotine degradation by Arthrobacter nicotinovorans, a Gram-positive soil bacterium, is linked to the presence of the catabolic megaplasmid pAO1. l-[(14)C]Nicotine uptake assays with A. nicotinovorans showed transport of nicotine across the cell membrane to be energy-independent and saturable with a K(m) of 6.2+/-0.1 microM and a V(max) of 0.70+/-0.08 micromol min(-1) (mg protein)(-1). This is in accord with a mechanism of facilitated diffusion, driven by the nicotine concentration gradient. Nicotine uptake was coupled to its intracellular degradation, and an A. nicotinovorans strain unable to degrade nicotine (pAO1(-)) showed no nicotine import. However, when the nicotine dehydrogenase genes were expressed in this strain, import of l-[(14)C]nicotine took place. A. nicotinovorans pAO1(-) and Escherichia coli were also unable to import 6-hydroxy-l-nicotine, but expression of the 6-hydroxy-l-nicotine oxidase gene allowed both bacteria to take up this compound. l-Nicotine uptake was inhibited by d-nicotine, 6-hydroxy-l-nicotine and 2-amino-l-nicotine, which may indicate transport of these nicotine derivatives by a common permease. Attempts to correlate nicotine uptake with pAO1 genes possessing similarity to amino acid transporters failed. In contrast to the situation at the blood-brain barrier, nicotine transport across the cell membrane by these bacteria was not by passive diffusion or active transport but by facilitated diffusion.

Diffusion parameter mapping with the combined intravoxel incoherent motion and kurtosis model using artificial neural networks at 3 T.

PubMed

Bertleff, Marco; Domsch, Sebastian; Weingärtner, Sebastian; Zapp, Jascha; O'Brien, Kieran; Barth, Markus; Schad, Lothar R

2017-12-01

Artificial neural networks (ANNs) were used for voxel-wise parameter estimation with the combined intravoxel incoherent motion (IVIM) and kurtosis model facilitating robust diffusion parameter mapping in the human brain. The proposed ANN approach was compared with conventional least-squares regression (LSR) and state-of-the-art multi-step fitting (LSR-MS) in Monte-Carlo simulations and in vivo in terms of estimation accuracy and precision, number of outliers and sensitivity in the distinction between grey (GM) and white (WM) matter. Both the proposed ANN approach and LSR-MS yielded visually increased parameter map quality. Estimations of all parameters (perfusion fraction f, diffusion coefficient D, pseudo-diffusion coefficient D*, kurtosis K) were in good agreement with the literature using ANN, whereas LSR-MS resulted in D* overestimation and LSR yielded increased values for f and D*, as well as decreased values for K. Using ANN, outliers were reduced for the parameters f (ANN, 1%; LSR-MS, 19%; LSR, 8%), D* (ANN, 21%; LSR-MS, 25%; LSR, 23%) and K (ANN, 0%; LSR-MS, 0%; LSR, 15%). Moreover, ANN enabled significant distinction between GM and WM based on all parameters, whereas LSR facilitated this distinction only based on D and LSR-MS on f, D and K. Overall, the proposed ANN approach was found to be superior to conventional LSR, posing a powerful alternative to the state-of-the-art method LSR-MS with several advantages in the estimation of IVIM-kurtosis parameters, which might facilitate increased applicability of enhanced diffusion models at clinical scan times. Copyright © 2017 John Wiley & Sons, Ltd.

Electrochemical Reduction of Oxygen in Aprotic Ionic Liquids Containing Metal Cations: A Case Study on the Na-O2 system.

PubMed

Azaceta, Eneko; Lutz, Lukas; Grimaud, Alexis; Vicent-Luna, Jose Manuel; Hamad, Said; Yate, Luis; Cabañero, German; Grande, Hans-Jurgen; Anta, Juan A; Tarascon, Jean-Marie; Tena-Zaera, Ramon

2017-04-10

Metal-air batteries are intensively studied because of their high theoretical energy-storage capability. However, the fundamental science of electrodes, electrolytes, and reaction products still needs to be better understood. In this work, the ionic liquid N-butyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) was chosen to study the influence of a wide range of metal cations (M n+ ) on the electrochemical behavior of oxygen. The relevance of the theory of Lewis hard and soft acids and bases to predict satisfactorily the reduction potential of oxygen in electrolytes containing metal cations is demonstrated. Systems with soft and intermediate M n+ acidity are shown to facilitate oxygen reduction and metal oxide formation, whereas oxygen reduction is hampered by hard acid cations such as sodium and lithium. Furthermore, DFT calculations on the energy of formation of the resulting metal oxides rationalize the effect of M n+ on oxygen reduction. A case study on the Na-O 2 system is described in detail. Among other things, the Na + concentration of the electrolyte is shown to control the electrochemical pathway (solution precipitation vs. surface deposition) by which the discharge product grows. All in all, fundamental insights for the design of advanced electrolytes for metal-air batteries, and Na-air batteries in particular, are provided. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Sorption of Cationic Surfactants to Artificial Cell Membranes: Comparing Phospholipid Bilayers with Monolayer Coatings and Molecular Simulations.

PubMed

Timmer, Niels; Droge, Steven T J

2017-03-07

This study reports the distribution coefficient between phospholipid bilayer membranes and phosphate buffered saline (PBS) medium (D MW,PBS ) for 19 cationic surfactants. The method used a sorbent dilution series with solid supported lipid membranes (SSLMs). The existing SSLM protocol, applying a 96 well plate setup, was adapted to use 1.5 mL glass autosampler vials instead, which facilitated sampling and circumvented several confounding loss processes for some of the cationic surfactants. About 1% of the phospholipids were found to be detached from the SSLM beads, resulting in nonlinear sorption isotherms for compounds with log D MW values above 4. Renewal of the medium resulted in linear sorption isotherms. D MW values determined at pH 5.4 demonstrated that cationic surfactant species account for the observed D MW,PBS . Log D MW,PBS values above 5.5 are only experimentally feasible with lower LC-MS/MS detection limits and/or concentrated extracts of the aqueous samples. Based on the number of carbon atoms, dialkylamines showed a considerably lower sorption affinity than linear alkylamine analogues. These SSLM results closely overlapped with measurements on a chromatographic tool based on immobilized artificial membranes (IAM-HPLC) and with quantum-chemistry based calculations with COSMOmic. The SSLM data suggest that IAM-HPLC underestimates the D MW of ionized primary and secondary alkylamines by 0.8 and 0.5 log units, respectively.

Automation of flow injection gas diffusion-ion chromatography for the nanomolar determination of methylamines and ammonia in seawater and atmospheric samples

PubMed Central

Gibb, Stuart W.; Wood, John W.; Fauzi, R.; Mantoura, C.

1995-01-01

The automation and improved design and performance of Flow Injection Gas Diffusion-Ion Chromatography (FIGD-IC), a novel technique for the simultaneous analysis of trace ammonia (NH3) and methylamines (MAs) in aqueous media, is presented. Automated Flow Injection Gas Diffusion (FIGD) promotes the selective transmembrane diffusion of MAs and NH3 from aqueous sample under strongly alkaline (pH > 12, NaOH), chelated (EDTA) conditions into a recycled acidic acceptor stream. The acceptor is then injected onto an ion chromatograph where NH3 and the MAs are fully resolved as their cations and detected conductimetrically. A versatile PC interfaced control unit and data capture unit (DCU) are employed in series to direct the selonoid valve switching sequence, IC operation and collection of data. Automation, together with other modifications improved both linearily (R2 > 0.99 MAs 0-100 nM, NH3 0-1000 nM) and precision (<8%) of FIGD-IC at nanomolar concentrations, compared with the manual procedure. The system was successfully applied to the determination of MAs and NH3 in seawater and in trapped particulate and gaseous atmospheric samples during an oceanographic research cruise. PMID:18925047

Wavy membranes and the growth rate of a planar chemical garden: Enhanced diffusion and bioenergetics.

PubMed

Ding, Yang; Batista, Bruno; Steinbock, Oliver; Cartwright, Julyan H E; Cardoso, Silvana S S

2016-08-16

To model ion transport across protocell membranes in Hadean hydrothermal vents, we consider both theoretically and experimentally the planar growth of a precipitate membrane formed at the interface between two parallel fluid streams in a 2D microfluidic reactor. The growth rate of the precipitate is found to be proportional to the square root of time, which is characteristic of diffusive transport. However, the dependence of the growth rate on the concentrations of hydroxide and metal ions is approximately linear and quadratic, respectively. We show that such a difference in ionic transport dynamics arises from the enhanced transport of metal ions across a thin gel layer present at the surface of the precipitate. The fluctuations in transverse velocity in this wavy porous gel layer allow an enhanced transport of the cation, so that the effective diffusivity is about one order of magnitude higher than that expected from molecular diffusion alone. Our theoretical predictions are in excellent agreement with our laboratory measurements of the growth of a manganese hydroxide membrane in a microfluidic channel, and this enhanced transport is thought to have been needed to account for the bioenergetics of the first single-celled organisms.

Molecular dynamics in stiff ionene below glass transition.

PubMed

Makrocka-Rydzyk, M; Glowinkowski, S; Jurga, S; Meyer, W H

1995-08-01

Temperature dependences of proton and fluorine second moments and spin-lattice relaxation time T1 below glass transition were measured in glassy "I-Do,Pip-Me-BF4" ionene. The existence of motions of methyl groups and segments linking the cationic centers, namely piperidinium rings and trimethylene groups, for the polymeric part of ionene were established. Isotropic rotation of the counter-ion was evidenced and its limited diffusion suggested. To interpret the proton and fluorine relaxation data, a Davidson-Cole distribution of correlation times was assumed.

Preliminary Evaluations of Polymer-based Lithium Battery Electrolytes Under Development for the Polymer Electrolyte Rechargeable Systems Program

NASA Technical Reports Server (NTRS)

Manzo, Michelle A.; Bennett, William R.

2003-01-01

A component screening facility has been established at The NASA Glenn Research Center (GRC) to evaluate candidate materials for next generation, lithium-based, polymer electrolyte batteries for aerospace applications. Procedures have been implemented to provide standardized measurements of critical electrolyte properties. These include ionic conductivity, electronic resistivity, electrochemical stability window, cation transference number, salt diffusion coefficient and lithium plating efficiency. Preliminary results for poly(ethy1ene oxide)-based polymer electrolyte and commercial liquid electrolyte are presented.

Polymers in separation processes

NASA Astrophysics Data System (ADS)

Wieszczycka, Karolina; Staszak, Katarzyna

2017-05-01

Application of polymer materials as membranes and ion-exchange resins was presented with a focus on their use for the recovery of metal ions from aqueous solutions. Several membrane techniques were described including reverse osmosis, nanofiltration, ultrafiltration, diffusion and Donnan dialysis, electrodialysis and membrane extraction system (polymer inclusion and supported membranes). Moreover, the examples of using ion-exchange resins in metal recovery were presented. The possibility of modification of the resin was discussed, including hybrid system with metal cation or metal oxide immobilized on polymer matrices or solvent impregnated resin.

Respirometric biomonitor for the control of industrial effluent toxicity

NASA Astrophysics Data System (ADS)

Campanella, Luigi; Favero, G.; Mastrofini, D.; Tomassetti, M.

1995-10-01

A yeast cell biosystem has been recently developed for the total toxicity testing of a sample that may contain a number of different polluting species. The method uses an amperometric gas diffusion oxygen sensor as indicating electrode and is based on the perturbation of the respiratory activity of the immobilized yeast Saccharomyces cerevisiae; glucose acts as substrate. Several toxic substances were tested: metal ions, phenol and cationic, anionic or nonionic surfactants. Some results of a monitoring program of an industrial wastewater are also reported and discussed.

Lithium ion insertion and extraction reactions with Hollandite-type manganese dioxide free from any stabilizing cations in its tunnel cavity

NASA Astrophysics Data System (ADS)

Kijima, Norihito; Takahashi, Yasuhiko; Akimoto, Junji; Awaka, Junji

2005-09-01

Lithium ion insertion and extraction reactions with a hollandite-type α-MnO 2 specimen free from any stabilizing cations in its tunnel cavity were investigated, and the crystal structure of a Li+-inserted α-MnO 2 specimen was analyzed by Rietveld refinement and whole-pattern fitting based on the maximum-entropy method (MEM). The pH titration curve of the α-MnO 2 specimen displayed a monobasic acid behavior toward Li+, and an ion-exchange capacity of 3.25 meq/g was achieved at pH>11. The Li/Mn molar ratio of the Li+-inserted α-MnO 2 specimen showed that about two Li+ ions can be chemically inserted into one unit cell of the hollandite-type structure. As the amount of Li content was increased, the lattice parameter a increased while c hardly changed. On the other hand, the mean oxidation number of Mn decreased slightly regardless of Li content whenever ions were exchanged. The Li+-inserted α-MnO 2 specimen reduced topotactically in one phase when it was used as an active cathode material in a liquid organic electrolyte (1:1 EC:DMC, 1 mol/dm 3 LiPF 6) lithium cell. An initial discharge with a capacity of approximately 230 mAh/g was achieved, and the reaction was reversible, whereas the capacity fell steadily upon cycling. About six Li+ ions could be electrochemically inserted into one unit cell of the hollandite-type structure. By contrast, the parent α-MnO 2 specimen showed a poor discharge property although no cationic residues or residual H 2O molecules remained in the tunnel space. Rietveld refinement from X-ray powder diffraction data for a Li+-inserted specimen of (Li 2O) 0.12MnO 2 showed it to have the hollandite-type structure (tetragonal; space group I4/m; a=9.993(11) and c=2.853(3) Å; Z=8; Rwp=6.12%, Rp=4.51%, RB=1.41%, and RF=0.79%; S=1.69). The electron-density distribution images in (Li 2O) 0.12MnO 2 showed that Li 2O molecules almost fill the tunnel space. These findings suggest that the presence of stabilizing atoms or molecules within the tunnel of a hollandite-type structure is necessary to facilitate the diffusion of Li+ ions during cycling.

Cylindrical diffuser performance using a truncated plug nozzle

NASA Technical Reports Server (NTRS)

Galanga, F. L.; Mueller, T. J.

1976-01-01

Cylindrical diffuser performance for a truncated plug nozzle without external flow was tested in a blowdown wind tunnel. The nozzle was designed for an exit Mach number of 1.9 and the plug was conical in shape from the throat and converged to the axis of symmetry at an angle of 10 degrees. The diffuser section was fashioned into two 13.97 cm lengths to facilitate boring of the duct diameter and to allow for testing of two different duct lengths. A slotted hypotube was installed in the base of the diffuser to measure pressure distribution down the centerline of the diffuser. The data obtained included: the typical centerline and sidewall pressure ratio variation along the diffuser, cell pressure ratio vs overall pressure ratio for long and short diffusers and a comparison of minimum experimental cell pressure ratio vs area ratio.

Sustained release of hepatocyte growth factor by cationic self-assembling peptide/heparin hybrid hydrogel improves β-cell survival and function through modulating inflammatory response

PubMed Central

Liu, Shuyun; Zhang, Lanlan; Cheng, Jingqiu; Lu, Yanrong; Liu, Jingping

2016-01-01

Inflammatory response is a major cause of grafts dysfunction in islet transplantation. Hepatocyte growth factor (HGF) had shown anti-inflammatory activity in multiple diseases. In this study, we aim to deliver HGF by self-assembling peptide/heparin (SAP/Hep) hybrid gel to protect β-cell from inflammatory injury. The morphological and slow release properties of SAPs were analyzed. Rat INS-1 β-cell line was treated with tumor necrosis factor α in vitro and transplanted into rat kidney capsule in vivo, and the viability, apoptosis, function, and inflammation of β-cells were evaluated. Cationic KLD1R and KLD2R self-assembled to nanofiber hydrogel, which showed higher binding affinity for Hep and HGF because of electrostatic interaction. Slow release of HGF from cationic SAP/Hep gel is a two-step mechanism involving binding affinity with Hep and molecular diffusion. In vitro and in vivo results showed that HGF-loaded KLD2R/Hep gel promoted β-cell survival and insulin secretion, and inhibited cell apoptosis, cytokine release, T-cell infiltration, and activation of NFκB/p38 MAPK pathways in β-cells. This study suggested that SAP/Hep gel is a promising carrier for local delivery of bioactive proteins in islet transplantation. PMID:27729786

The influence of aliovalent impurities on the oxidation kinetics of nickel at high temperatures

NASA Astrophysics Data System (ADS)

Mrowec, S.; Grzesik, Z.; Rajchel, B.; Gil, A.; Dabek, J.

2005-01-01

The influence of chromium and sodium on the nickel oxidation kinetics has been studied as a function of temperature (1373-1673 K) and oxygen activity (10-105 Pa O2), using microthermogravimetric techniques. It has been shown that the oxidation of Ni-Cr and Ni-Na alloys, like that of pure nickel, follows strictly the parabolic rate law being thus diffusion controlled. In agreement with the defect model of Ni1-yO, it has been found that the oxidation rate of the Ni-Cr alloy is higher than that of pure nickel, the reaction rate is pressure independent and the activation energy of this process is lower. This implies that the concentration of double ionized cation vacancies in a Ni1-yO-Cr2O3 solid solution is fixed on a constant level by trivalent chromium ions, substitutionally incorporated into the cation sublattice of this oxide. In the case of the Ni-Na alloy, on the other hand, the oxidation rate is lower than that of pure nickel, the activation energy is higher and the oxidation rate increases more rapidly with oxygen pressure. These results can again be explained in terms of the doping effect, by assuming that univalent sodium ions dissolve substitutionally in the cation sublattice of nickel oxide.

Interfacial Redox Reactions Associated Ionic Transport in Oxide-Based Memories.

PubMed

Younis, Adnan; Chu, Dewei; Shah, Abdul Hadi; Du, Haiwei; Li, Sean

2017-01-18

As an alternative to transistor-based flash memories, redox reactions mediated resistive switches are considered as the most promising next-generation nonvolatile memories that combine the advantages of a simple metal/solid electrolyte (insulator)/metal structure, high scalability, low power consumption, and fast processing. For cation-based memories, the unavailability of in-built mobile cations in many solid electrolytes/insulators (e.g., Ta 2 O 5 , SiO 2 , etc.) instigates the essential role of absorbed water in films to keep electroneutrality for redox reactions at counter electrodes. Herein, we demonstrate electrochemical characteristics (oxidation/reduction reactions) of active electrodes (Ag and Cu) at the electrode/electrolyte interface and their subsequent ions transportation in Fe 3 O 4 film by means of cyclic voltammetry measurements. By posing positive potentials on Ag/Cu active electrodes, Ag preferentially oxidized to Ag + , while Cu prefers to oxidize into Cu 2+ first, followed by Cu/Cu + oxidation. By sweeping the reverse potential, the oxidized ions can be subsequently reduced at the counter electrode. The results presented here provide a detailed understanding of the resistive switching phenomenon in Fe 3 O 4 -based memory cells. The results were further discussed on the basis of electrochemically assisted cations diffusions in the presence of absorbed surface water molecules in the film.

Effects of variation in chain length on ternary polymer electrolyte - Ionic liquid mixture - A molecular dynamics simulation study

NASA Astrophysics Data System (ADS)

Raju, S. G.; Hariharan, Krishnan S.; Park, Da-Hye; Kang, HyoRang; Kolake, Subramanya Mayya

2015-10-01

Molecular dynamics (MD) simulations of ternary polymer electrolyte - ionic liquid mixtures are conducted using an all-atom model. N-alkyl-N-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide ([CnMPy][TFSI], n = 1, 3, 6, 9) and polyethylene oxide (PEO) are used. Microscopic structure, energetics and dynamics of ionic liquid (IL) in these ternary mixtures are studied. Properties of these four pure IL are also calculated and compared to that in ternary mixtures. Interaction between pyrrolidinium cation and TFSI is stronger and there is larger propensity of ion-pair formation in ternary mixtures. Unlike the case in imidazolium IL, near neighbor structural correlation between TFSI reduces with increase in chain length on cation in both pure IL and ternary mixtures. Using spatial density maps, regions where PEO and TFSI interact with pyrrolidinium cation are identified. Oxygens of PEO are above and below the pyrrolidinium ring and away from the bulky alkyl groups whereas TFSI is present close to nitrogen atom of CnMPy. In pure IL, diffusion coefficient (D) of C3MPy is larger than of TFSI but D of C9MPy and C6MPy are larger than that of TFSI. The reasons for alkyl chain dependent phenomena are explored.

Health Promotion Efforts as Predictors of Physical Activity in Schools: An Application of the Diffusion of Innovations Model

ERIC Educational Resources Information Center

Glowacki, Elizabeth M.; Centeio, Erin E.; Van Dongen, Daniel J.; Carson, Russell L.; Castelli, Darla M.

2016-01-01

Background: Implementing a comprehensive school physical activity program (CSPAP) effectively addresses public health issues by providing opportunities for physical activity (PA). Grounded in the Diffusion of Innovations model, the purpose of this study was to identify how health promotion efforts facilitate opportunities for PA. Methods: Physical…

Innovation for the Common Man: Avoiding the Pitfalls of Implementing New Technologies.

ERIC Educational Resources Information Center

Troxel, Steve

Citing the failure of film, radio, and television to revolutionize the American education system, this paper identifies reasons for those failures and suggests ways to avoid similar failure in the diffusion of computer use in education and the diffusion of "datafication" into the homes of rural America. Four steps are identified to facilitate the…

Facilitating Changes in Ninth Grade Students' Understanding of Dissolution and Diffusion through DSLM Instruction

ERIC Educational Resources Information Center

She, Hsiao-Ching

2004-01-01

This study examines the nature and process of ninth grade students' conceptual change regarding their mental model of dissolution and diffusion as a result of instructions using the Dual Situated Learning Model (DSLM). The dual situated learning events of this model are designed according to the students' ontological viewpoint of the science…

Singlet and doublet states UV-vis spectrum and electronic properties of 3-methylchrysene and 4-methylchrysene in glass matrix.

PubMed

Husain, Mudassir M; Tandon, H C; Varadwaj, Pradeep R

2008-03-01

The ultraviolet-visual spectrum of 3-methylchrysene, 4-methylchrysene and their radical cations formed by ultraviolet radiations, were measured in glass matrix at the room temperature. In the measured singlet state spectrum we were able to identify the alpha, p, beta, beta' (Clar's) or (1)L(b), (1)L(a)(1)B(b), (1)B(a) (Platt's notation) bands. The presence of alpha, beta or (1)L(b), (1)B(b) was confirmed by calculating their wavelength ratio lambda(alpha)/lambda(beta). Since matrix induces perturbation in the measured spectrum; it becomes necessary to take into account the perturbation while computing the spectrum. An effort has been made in this work to simulate the electronic spectrum in the same environment as is measured. This study presents the first calculated spectrum of these systems and their cations in glass matrix by semi empirical methods. To observe the magnitude of perturbation and hence to see the spectral shift in glass matrix, the spectrum was calculated in the free state as well. Spectral properties such as frontier orbitals gap, dipole moment, mean polarizabilities and its tensors were also computed both in glass matrix and free state using semiemperical method. The measured bands of 3-methylchrysene cation at wavelength 416.50 and 473.85 nm closely match with the available diffuse intersteallar bands (DIBs) at 417.55 and 472.64 nm, respectively. Also the observed 474.85 nm band of 4-methylchrysene cation matches the DIB at 476.00 nm.

Experimental Electronic Spectroscopy of Two PAHs: Naphthalene and 2-METHYL Naphthalene

NASA Astrophysics Data System (ADS)

Friha, H.; Feraud, G.; Pino, T.; Brechignac, Ph.; Parneix, P.; Dhaoudi, Z.; Jaidane, N.; Galila, H.; Troy, T.; Schmidt, T.

2011-06-01

The presence of polycyclic aromatic hydrocarbons (PAHs) in the interstellar medium (ISM) was suggested in the mid-80's. Since then, their important role in the physico-chemical evolution of the ISM has been confirmed. Interstellar PAHs have been in particular proposed as possible carriers of some Diffuse Interstellar Bands (DIBs). These absorption bands are seen in the spectra of reddened stars from the visible to the near infrared and constitute a major astrophysical issue. Our purpose is to obtain electronic spectra of gas phase PAHs which will be used to probe their participation to the interstellar extinction curve from the visible (DIBs) to the UV (bump). For this goal PAHs cations represent an excellent set of target species. A new way of forming PAH+-Ar_n clusters cations has been implemented in the experimental set-up 'ICARE' at ISMO (Orsay) giving us the capability to measure the electronic spectra of cold PAH cations in the gas phase through the "Ar tagging" trick. Two molecules have been investigated in this way: naphthalene (C_1_0H_8) and 2- methyl naphthalene (C_1_1H_1_0). Clusters of naphthalene and (or 2-methyl-naphthalene) with Ar atoms are first formed in a supersonic jet, before being hit by a 281 nm laser beam which photo-ionizes the clusters which are then injected in a molecular beam through a skimmer. A tunable laser beam crossing downstream photo-dissociates the cations. The bare PAH fragments are detected using a Time-Of-Flight spectrometer while scanning the visible laser wavelength from 470 to 690 nm.

A conformationally persistent pseudo-bicyclic guanidinium for anion coordination as stabilized by dual intramolecular hydrogen bonds

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seipp, Charles A.; Williams, Neil J.; Bryantsev, Vyacheslav S.

2015-11-30

In this paper, the first example of a pseudo-bicyclic guanidinium ligand is reported. When bound to an anion, the N,N'-bis(2-pyridyl)guanidinium cation persistently adopts the planar α,α conformation featuring intramolecular N···H–N–H···N hydrogen bonds in the solid state, which facilitates crystallization of sulphate from aqueous mixtures of anions.

Formation of artificial granules for proving gelation as the main mechanism of aerobic granulation in biological wastewater treatment.

PubMed

Li, Yun; Yang, Shu-Fang; Zhang, Jian-Jun; Li, Xiao-Yan

2014-01-01

In this study, gelation-facilitated biofilm formation as a new mechanism is proposed for the phenomenon of aerobic granulation in biological wastewater treatment. To obtain an experimental proof for the gelation-based theory, the granulation process was simulated in a chemical system using latex particles for bacterial cells and organic polymers (alginate and peptone) for extracellular polymeric substances (EPS) in a solution with the addition of cations (Ca²⁺, Mg²⁺ and Fe³⁺). The results showed that at a low alginate content (70 mg g⁻¹ mixed liquid suspended solids (MLSS)) flocculation was observed in the suspension with loose flocs. At a higher alginate content (180 mg g⁻¹ MLSS), together with discharge of small flocs, formation of artificial gel granules was successfully achieved leading to granulation. The artificial granules show a morphological property similar to that of actual microbial granules. However, if the protein content increased, granulation became difficult with little gel formation. The experimental work demonstrates the importance of the bonding interactions between EPS functional groups and cations in gel formation and granulation. The laboratory results on the formation of artificial granules provide a sound proof for the theory of gelation-facilitated biofilm formation as the main mechanism for aerobic granulation in sludge suspensions.

Diffusion in Brain Extracellular Space

PubMed Central

Syková, Eva; Nicholson, Charles

2009-01-01

Diffusion in the extracellular space (ECS) of the brain is constrained by the volume fraction and the tortuosity and a modified diffusion equation represents the transport behavior of many molecules in the brain. Deviations from the equation reveal loss of molecules across the blood-brain barrier, through cellular uptake, binding or other mechanisms. Early diffusion measurements used radiolabeled sucrose and other tracers. Presently, the real-time iontophoresis (RTI) method is employed for small ions and the integrative optical imaging (IOI) method for fluorescent macromolecules, including dextrans or proteins. Theoretical models and simulations of the ECS have explored the influence of ECS geometry, effects of dead-space microdomains, extracellular matrix and interaction of macromolecules with ECS channels. Extensive experimental studies with the RTI method employing the cation tetramethylammonium (TMA) in normal brain tissue show that the volume fraction of the ECS typically is about 20% and the tortuosity about 1.6 (i.e. free diffusion coefficient of TMA is reduced by 2.6), although there are regional variations. These parameters change during development and aging. Diffusion properties have been characterized in several interventions, including brain stimulation, osmotic challenge and knockout of extracellular matrix components. Measurements have also been made during ischemia, in models of Alzheimer's and Parkinson's diseases and in human gliomas. Overall, these studies improve our conception of ECS structure and the roles of glia and extracellular matrix in modulating the ECS microenvironment. Knowledge of ECS diffusion properties are valuable in contexts ranging from understanding extrasynaptic volume transmission to the development of paradigms for drug delivery to the brain. PMID:18923183

The role of external and internal mass transfer in the process of Cu2+ removal by natural mineral sorbents.

PubMed

Sljivić, M; Smiciklas, I; Plećas, I; Pejanović, S

2011-07-01

The kinetics of Cu2+ sorption on to zeolite, clay and diatomite was investigated as a function of initial metal concentrations. For consideration of the mass transfer phenomena, single resistance models based on both film and intraparticle diffusion were tested and compared. The obtained results suggested that the rate-limiting step in Cu2+ sorption strongly depended on the sorbent type, as well as on initial cation concentration. The decrease in external mass transfer coefficients with the increase in initial metal concentrations was in excellent agreement with expressions based on Sherwood and Schmidt dimensionless numbers. The internal diffusivities through zeolite particles were in the range 1.0 x 10(-11) to 1.0 x 10(-13) m2/min, depending on the Cu2+ concentration and the applied theoretical model.

Studies on the electrodeposition of tin from acidic chloride-gluconate solutions

NASA Astrophysics Data System (ADS)

Rudnik, Ewa; Włoch, Grzegorz

2013-01-01

Electrodeposition of tin from acidic chloride-gluconate baths was investigated. Equilibrium distribution of tin(II) species showed domination of Sn(II)-gluconate complexes, but for Sn2+ concentrations 50 mM or higher increased percentage of Sn(II)-chloride complexes was found. Cyclic voltammetry, anodic stripping analysis and potentiostatic measurements indicated that rate of the cathodic process is determined by the release of metal cations from gluconate complexes in diluted bath (5 mM), but for more concentrated solutions reduction of Sn(II) ions run under diffusion control. Studies of anodic response showed that it depends on the Sn(II)/Glu ratio in the bath and deposition potential due to development of different planes of metal crystal. Average effective diffusion coefficients of metal species were determined. Morphology and structure tin deposits were also presented.

The Fe2(+)-Mg interdiffusion in orthopyroxene: Constraints from cation ordering and structural data and implications for cooling rates of meteorites

NASA Technical Reports Server (NTRS)

Ganguly, J.; Tazzoli, V.

1993-01-01

Orthopyroxene crystals in a number of meteorites exhibit compositional zoning of Fe and Mg, which provide important constraint on their cooling rates. However, attempts to model cooling rate of these crystals from Fe-Mg zoning profiles suffer from the lack of any measured or theoretically well constrained Fe-Mg interdiffusion data in OP(x) It has been assumed that Fe-Mg interdiffusion in OP(x) only slightly slower than that in olivine. The purpose of this paper is to (1) calculate the Fe-Mg fractionation, and (2) provide analytical formulation relating cooling rate to the length of the diffusion zone across the interface of the overgrowth of a mineral on itself with application to Mg diffusion profile across OP(x) growth on OP(x) in certain mesosiderites.

Memantine transport across the mouse blood-brain barrier is mediated by a cationic influx H+ antiporter.

PubMed

Mehta, Dharmini C; Short, Jennifer L; Nicolazzo, Joseph A

2013-12-02

Memantine (MEM) is prescribed in mono and combination therapies for treating the symptoms of moderate to severe Alzheimer's disease (AD). Despite MEM being widely prescribed with other AD and non-AD medicines, very little is known about its mechanism of transport across the blood-brain barrier (BBB), and whether the nature of this transport lends MEM to a potential for drug-drug interactions at the BBB. Therefore, the purpose of this study was to characterize the mechanisms facilitating MEM brain uptake in Swiss Outbred mice using an in situ transcardiac perfusion technique, and identify the putative transporter involved in MEM disposition into the brain. Following transcardiac perfusion of MEM with increasing concentrations, the brain uptake of MEM was observed to be saturable. Furthermore, MEM brain uptake was reduced (up to 55%) by various cationic transporter inhibitors (amantadine, quinine, tetraethylammonium, choline and carnitine) and was dependent on extracellular pH, while being independent of membrane depolarization and the presence of Na(+) in the perfusate. In addition, MEM brain uptake was observed to be sensitive to changes in intracellular pH, hence, likely to be driven by H(+)/MEM antiport mechanisms. Taken together, these findings implicate the involvement of an organic cation transporter regulated by proton antiport mechanisms in the transport of MEM across the mouse BBB, possibly the organic cation/carnitine transporter, OCTN1. These studies also clearly demonstrate the brain uptake of MEM is significantly reduced by other cationic compounds, highlighting the need to consider the possibility of drug interactions with MEM at the BBB, potentially leading to reduced brain uptake and, therefore, altered efficacy of MEM when used in patients on multidrug regimens.

Simulation of a cellulose fiber in ionic liquid suggests a synergistic approach to dissolution

DOE PAGES

Mostofian, Barmak; Smith, Jeremy C.; Cheng, Xiaolin

2013-08-11

Ionic liquids dissolve cellulose in a more efficient and environmentally acceptable way than conventional methods in aqueous solution. An understanding of how ionic liquids act on cellulose is essential for improving pretreatment conditions and thus detailed knowledge of the interactions between the cations, anions and cellulose is necessary. Here in this study, to explore ionic liquid effects, we perform all-atom molecular dynamics simulations of a cellulose microfibril in 1-butyl-3-methylimidazolium chloride and analyze site–site interactions and cation orientations at the solute–solvent interface. The results indicate that Cl - anions predominantly interact with cellulose surface hydroxyl groups but with differences between chainsmore » of neighboring cellulose layers, referred to as center and origin chains; Cl- binds to C3-hydroxyls on the origin chains but to C2- and C6-hydroxyls on the center chains, thus resulting in a distinct pattern along glucan chains of the hydrophilic fiber surfaces. In particular, Cl - binding disrupts intrachain O3H–O5 hydrogen bonds on the origin chains but not those on the center chains. In contrast, Bmim + cations stack preferentially on the hydrophobic cellulose surface, governed by non-polar interactions with cellulose. Complementary to the polar interactions between Cl - and cellulose, the stacking interaction between solvent cation rings and cellulose pyranose rings can compensate the interaction between stacked cellulose layers, thus stabilizing detached cellulose chains. Moreover, a frequently occurring intercalation of Bmim + on the hydrophilic surface is observed, which by separating cellulose layers can also potentially facilitate the initiation of fiber disintegration. The results provide a molecular description why ionic liquids are ideal cellulose solvents, the concerted action of anions and cations on the hydrophobic and hydrophilic surfaces being key to the efficient dissolution of the amphiphilic carbohydrate.« less

Reduced Hepatic Uptake and Intestinal Excretion of Organic Cations in Mice with a Targeted Disruption of the Organic Cation Transporter 1 (Oct1 [Slc22a1]) Gene

PubMed Central

Jonker, Johan W.; Wagenaar, Els; Mol, Carla A. A. M.; Buitelaar, Marije; Koepsell, Hermann; Smit, Johan W.; Schinkel, Alfred H.

2001-01-01

The polyspecific organic cation transporter 1 (OCT1 [SLC22A1]) mediates facilitated transport of small (hydrophilic) organic cations. OCT1 is localized at the basolateral membrane of epithelial cells in the liver, kidney, and intestine and could therefore be involved in the elimination of endogenous amines and xenobiotics via these organs. To investigate the pharmacologic and physiologic role of this transport protein, we generated Oct1 knockout (Oct1−/−) mice. Oct1−/− mice appeared to be viable, healthy, and fertile and displayed no obvious phenotypic abnormalities. The role of Oct1 in the pharmacology of substrate drugs was studied by comparing the distribution and excretion of the model substrate tetraethylammonium (TEA) after intravenous administration to wild-type and Oct1−/− mice. In Oct1−/− mice, accumulation of TEA in liver was four to sixfold lower than in wild-type mice, whereas direct intestinal excretion of TEA was reduced about twofold. Excretion of TEA into urine over 1 h was 53% of the dose in wild-type mice, compared to 80% in knockout mice, probably because in Oct1−/− mice less TEA accumulates in the liver and thus more is available for rapid excretion by the kidney. In addition, we found that absence of Oct1 leads to decreased liver accumulation of the anticancer drug metaiodobenzylguanidine and the neurotoxin 1-methyl-4-phenylpyridium. In conclusion, our data show that Oct1 plays an important role in the uptake of organic cations into the liver and in their direct excretion into the lumen of the small intestine. PMID:11463829

An intrinsically fluorescent dendrimer as a nanoprobe of cell transport.

PubMed

Al-Jamal, Khuloud T; Ruenraroengsak, Pakatip; Hartell, Nicholas; Florence, Alexander T

2006-07-01

Dendrimers, spherical or quasi-spherical synthetic polymers in the nano-size range, have found useful applications as prospective carriers in drug and gene delivery. The investigation of dendrimer uptake by cells has been previously achieved by the incorporation of a fluorescent dye to the dendrimer either by chemical conjugation or by physical interaction. Here we describe the synthesis of two intrinsically fluorescent lysine based cationic dendrimers which lack a fluorophore, but which has sufficient fluorescence intensity to be detected at low concentrations. The nomenclature used to describe our compounds results in, for example the 6th generation dendrimer being notated as Gly-Lys(63) (NH2)(64); Gly denotes that the compound has a glycine in the core coupled to 63 lysine branching units (Lys(63)) and that the surface has 64 free amino groups (NH2)(64). The use of these dendrimers in probing transport avoids the need for fluorescent tagging with its attendant problems. The uptake of Gly-Lys(63) (NH2)(64) into Caco-2 cells was followed using confocal microscopy. Being cationic, it first adsorbs to the cell surface, enters the cytoplasm and reaches the nucleus within 35-45 min. Estimates of the diffusion coefficient of the dendrimer within the cell cytoplasm leads to a value of 6.27 ( +/- 0.49) x 10(-11) cm(2) s(-1), which is up to 1000 times lower than the diffusion coefficient of the dendrimer in water. Intrinsically fluorescent dendrimers of different size and charge are useful probes of transport in cells.

Oxidation of a Commercial Nickel-Based Superalloy under Static Loading

NASA Astrophysics Data System (ADS)

Foss, B. J.; Hardy, M. C.; Child, D. J.; McPhail, D. S.; Shollock, B. A.

2014-12-01

The current demands of the aviation industry for increased gas-turbine efficiency necessitate higher turbine entry temperatures, requiring that alloys exhibit superior oxidation resistance. The synergistic effects of oxidation and mechanical stresses pose a complex issue. The purpose of the current research was to examine the effects of stress on the oxidation and oxygen transport in a commercial nickel-based superalloy. Fine grain RR1000 in both polished and shot-peened conditions was studied for classic (zero load) and statically loaded conditions using integrated two-stage isotopic tracing combined with focused-ion-beam secondary ion mass spectrometry (FIB-SIMS). Cr2O3 external oxide formed with semicontinuous TiO2 above and below. Preferential grain boundary Al2O3 internal oxide formation, γ'-dissolution, and recrystallization occurred subsurface. Oxidation mechanisms were dominated by anionic/cationic growth in the external oxide with inward oxygen transport, initially through the partially unprotective external oxide, then along internal oxide/alloy interfaces. Loading did not influence the oxidation products formed but did bring about expedited oxidation kinetics and changes to the oxide morphology. The oxygen diffusivity D {O/ * } (×10-13 cm2s-1) ranged from 0.39 for the polished alloy to 3.7 for the shot-peened condition under compressive stress. Arguably, the most significant effects took place in the subsurface regions. Increased oxidation kinetics were attributed to the development of fast cation diffusion paths as the alloy deformed by creep.

Interfacial water on crystalline silica: a comparative molecular dynamics simulation study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ho, Tuan A.; Argyris, Dimitrios; Papavassiliou, Dimitrios V.

2011-03-03

All-atom molecular dynamics simulations were conducted to study the dynamics of aqueous electrolyte solutions confined in slit-shaped silica nanopores of various degrees of protonation. Five degrees of protonation were prepared by randomly removing surface hydrogen atoms from fully protonated crystalline silica surfaces. Aqueous electrolyte solutions containing NaCl or CsCl salt were simulated at ambient conditions. In all cases, the ionic concentration was 1 M. The results were quantified in terms of atomic density distributions within the pores, and the self-diffusion coefficient along the direction parallel to the pore surface. We found evidence for ion-specific properties that depend on ion surface,more » water ion, and only in some cases ion ion correlations. The degree of protonation strongly affects the structure, distribution, and the dynamic behavior of confined water and electrolytes. Cl ions adsorb on the surface at large degrees of protonation, and their behavior does not depend significantly on the cation type (either Na+ or Cs+ ions are present in the systems considered). The cations show significant ion-specific behavior. Na+ ions occupy different positions within the pore as the degree of protonation changes, while Cs+ ions mainly remain near the pore center at all conditions considered. For a given degree of protonation, the planar self-diffusion coefficient of Cs+ is always greater than that of Na+ ions. The results are useful for better understanding transport under confinement, including brine behavior in the subsurface, with important applications such as environmental remediation.« less

B-Site Cation-Ordered Double-Perovskite Oxide as an Outstanding Electrode Material for Supercapacitive Energy Storage Based on the Anion Intercalation Mechanism.

PubMed

Xu, Zhenye; Liu, Yu; Zhou, Wei; Tade, Moses O; Shao, Zongping

2018-03-21

Perovskite oxides are highly promising electrodes for oxygen-ion-intercalation-type supercapacitors owing to their high oxygen vacancy concentration, oxygen diffusion rate, and tap density. Based on the anion intercalation mechanism, the capacitance is contributed by surface redox reactions and oxygen ion intercalation in the bulk materials. A high concentration of oxygen vacancies is needed because it is the main charge carrier. In this study, we propose a B-site cation-ordered Ba 2 Bi 0.1 Sc 0.2 Co 1.7 O 6-δ as an electrode material with an extremely high oxygen vacancy concentration and oxygen diffusion rate. A maximum capacitance of 1050 F g -1 was achieved, and a high capacitance of 780 F g -1 was maintained even after 3000 charge-discharge cycles at a current density of 1 A g -1 with an aqueous alkaline solution (6 M KOH) electrolyte, indicating an excellent cycling stability. In addition, the specific volumetric capacitance of Ba 2 Bi 0.1 Sc 0.2 Co 1.7 O 6-δ reaches up to 2549.4 F cm -3 based on the dense construction and high tap density (3.2 g cm -3 ). In addition, an asymmetric supercapacitor was constructed using activated carbon as a negative electrode, and it displayed the highest specific energy density of 70 Wh kg -1 at the power density of 787 W kg -1 in this study.

Polycyclic aromatic hydrocarbon ions and the diffuse interstellar bands

NASA Technical Reports Server (NTRS)

Salama, F.; Allamandola, L. J.

1995-01-01

Neutral naphthalene (C10H8), phenanthrene (C14H10), and pyrene (C16H10) absorb strongly in the ultraviolet and may contribute to the extinction curve. High abundances are required to produce detectable structures. The cations of these Polycyclic Aromatic Hydrocarbons (PAHs) absorb in the visible. C10H8(+) has 12 discrete absorption bands which fall between 6800 and 5000 A. The strongest band at 6741 A falls close to the weak 6742 A diffuse interstellar band (DIB). Five other weaker bands also match DIBs. The possibility that C10H8(+) is responsible for some of the DIBs can be tested by searching for new DIBS at 6520, 6151, and 5965 A, other moderately strong naphthalene cation band positions. If C10H8(+) is indeed responsible for the 6742 A feature, it accounts for 0.3% of the cosmic carbon. The spectrum of C16H10(+) is dominated by a strong band at 4435 A in an Ar matrix and 4395 A in a Ne matrix, a position which falls very close to the strongest DIB, that at 4430 A. If C16H10(+), or a closely related pyrene-like ion is indeed responsible for the 4430 A feature, it accounts for 0.2% of the cosmic carbon. We also report an intense, very broad UV-to-visible continuum which is associated with both ions and could explain how PAHs convert interstellar UV and visible radiation into IR.

Neutral and ionized polycyclic aromatic hydrocarbons, diffuse interstellar bands and the ultraviolet extinction curve

NASA Technical Reports Server (NTRS)

Salama, Farid; Allamandola, Louis John

1993-01-01

Neutral naphthalene C10H8, phenanthrene C14H10 and pyrene C16H10 absorb strongly in the ultraviolet region and may contribute to the extinction curve. High abundances are required to produce detectable structures. The cations of these polycyclic aromatic hydrocarbons (PAHs) absorb in the visible C10H8(+) has 13 discrete absorption bands which fall between 6800 and 4500 A. The strongest band at 6741 A falls close to the weak 6742 A diffuse interstellar band (DIB). Five other weaker bands also match DIBs. The possibility that C10H8(+) is responsible for some of the DIBs can be tested by searching for new DIBs at 6520 and 6151 A, other strong naphthalene cation band positions. If C10H8(+) is indeed responsible for the 6742 A feature, it accounts for 0.3% of the cosmic carbon. The spectrum of C16H10(+) is dominated by a strong band at 4435 A in an Ar matrix and 4395 A in Ne, wavelengths which fall very close to the strongest DIB at 4430 A. If C16H10(+) or a closely related pyrene-like ion, is indeed responsible for the 4430 A feature, it accounts for 0.2% of the cosmic carbon. An intense, very broad UV-to-visible continuum is reported which is associated with both ions and could explain how PAHs convert interstellar UV and visible radiation into IR radiation.

Ion migration in crystalline and amorphous HfOX

NASA Astrophysics Data System (ADS)

Schie, Marcel; Müller, Michael P.; Salinga, Martin; Waser, Rainer; De Souza, Roger A.

2017-03-01

The migration of ions in HfOx was investigated by means of large-scale, classical molecular-dynamics simulations over the temperature range 1000 ≤T /K ≤2000 . Amorphous HfOx was studied in both stoichiometric and oxygen-deficient forms (i.e., with x = 2 and x = 1.9875); oxygen-deficient cubic and monoclinic phases were also studied. The mean square displacement of oxygen ions was found to evolve linearly as a function of time for the crystalline phases, as expected, but displayed significant negative deviations from linear behavior for the amorphous phases, that is, the behavior was sub-diffusive. That oxygen-ion migration was observed for the stoichiometric amorphous phase argues strongly against applying the traditional model of vacancy-mediated migration in crystals to amorphous HfO2. In addition, cation migration, whilst not observed for the crystalline phases (as no cation defects were present), was observed for both amorphous phases. In order to obtain activation enthalpies of migration, the residence times of the migrating ions were analyzed. The analysis reveals four activation enthalpies for the two amorphous phases: 0.29 eV, 0.46 eV, and 0.66 eV (values very close to those obtained for the monoclinic structure) plus a higher enthalpy of at least 0.85 eV. In comparison, the cubic phase is characterized by a single value of 0.43 eV. Simple kinetic Monte Carlo simulations suggest that the sub-diffusive behavior arises from nanoscale confinement of the migrating ions.

Composites of cationic nanofibrillated cellulose and layered silicates: water vapor barrier and mechanical properties.

PubMed

Ho, Thao T T; Zimmermann, Tanja; Ohr, Steffen; Caseri, Walter R

2012-09-26

Composites of trimethylammonium-modified nanofibrillated cellulose and layered silicates (TMA-NFC/LS) were prepared by high-shear homogenization followed by pressure filtration and vacuum hot-pressing, which gave rise to particularly homogeneous dispersion of the silicate particles. Thirteen different clays and micas were employed. Water vapor barrier and mechanical properties (tensile strength, E-modulus, strain at break) of the composite films were investigated, considering the effects of layered silicate types and their concentration (in the range of 0 to 85 wt %). Good interactions between TMA-NFC and LS were obtained due to electrostatic attraction between cationic fibrils and anionic silicate layers, and even favored by high-shear homogenization process. Furthermore, oriented TMA-NFC/LS composite structure was achieved. Layered silicates exerted a pronounced influence on the water vapor barrier and mechanical properties; however, there was no common trend reflecting their types. The transport of water molecules through TMA-NFC/LS composites was studied considering both diffusion and adsorption mechanisms. As a result, diffusion pathways were proposed based on two new and one well-known models: the "native network", "covered fiber composite", and "fiber-brick composite" models. Importantly, it was found that the insertion of layered silicate particles did not improve automatically the barrier properties as indicated by the commonly used "fiber-brick composite" model. Mica R120 at a 50 wt % loading in composites with TMA-NFC matrix showed 30-fold improved water vapor permeability and 5-fold higher E-modulus compared to commercially used base paper.

Excited-State Proton Transfer on the Surface of a Therapeutic Protein, Protamine.

PubMed

Awasthi, Ankur A; Singh, Prabhat K

2017-11-16

Proton transfer reactions on biosurfaces play an important role in a myriad of biological processes. Herein, the excited-state proton transfer reaction of 8-hydroxypyrene-1,3,6-trisulfonate (HPTS) has been investigated in the presence of an important therapeutic protein, Protamine (PrS), using ground-state absorption, steady-state, and detailed time-resolved emission measurements. HPTS forms a 1:1 complex with Protamine with a high association constant of 2.6 × 10 4 M -1 . The binding of HPTS with Protamine leads to a significant modulation in the ground-state prototropic equilibrium causing a downward shift of 1.1 unit in the acidity constant (pK a ). In contrast to a large number of reports of slow proton transfer of HPTS on biosurfaces, interestingly, HPTS registers a faster proton transfer event in the presence of Protamine as compared to that of even the bulk aqueous buffer medium. Furthermore, the dimensionality of the proton diffusion process is also significantly reduced on the surface of Protamine that is in contrast to the behavior of HPTS in the bulk aqueous buffer medium, where the proton diffusion process is three-dimensional. The effect of ionic strength on the binding of HPTS toward PrS suggests a predominant role of electrostatic interaction between anionic HPTS and cationic Protamine, which is further supported by molecular docking simulations which predict that the most preferable binding site for HPTS on the surface of Protamine is surrounded by multiple cationic arginine residues.

Investigation of Sorption and Diffusion Mechanisms, and Preliminary Economic Analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhave, Ramesh R.; Jubin, Robert Thomas; Spencer, Barry B.

This report describes the synthesis and evaluation of molecular sieve zeolite membranes to separate and concentrate tritiated water (HTO) from dilute HTO-bearing aqueous streams. Several monovalent and divalent cation exchanged silico alumino phosphate (SAPO-34) molecular sieve zeolite membranes were synthesized on disk supports and characterized with gas and vapor permeation measurements. The pervaporation process performance was evaluated for the separation and concentration of tritiated water. Experiments were performed using tritiated water feed solution containing tritium at the high end of the range (1 mCi/mL) anticipated in a nuclear fuel processing system that includes both acid and water streams recycling. Themore » tritium concentration was about 0.1 ppm. The permeate was recovered under vacuum. The HTO/H2O selectivity and separation factor calculated from the measured tritium concentrations ranged from 0.99 to 1.23, and 0.83-0.98, respectively. Although the membrane performance for HTO separation was lower than expected, several encouraging observations including molecular sieving and high vapor permeance are reported. Additionally, several new approaches are proposed, such as tuning the sorption and diffusion properties offered by small pore LTA zeolite materials, and cation exchanged aluminosilicates with high metal loading. It is hypothesized that substantially improved preferential transport of tritium (HTO) resulting in a more concentrated permeate can be achieved. Preliminary economic analysis for the membrane-based process to concentrate tritiated water is also discussed.« less

Distribution of Gd(III) ions at the graphene oxide/water interface.

PubMed

Amirov, Rustem R; Shayimova, Julia; Dimiev, Ayrat M

2018-10-01

Graphene oxide (GO) have emerged recently as a novel material for sorbing metal cations from aqueous media. However, the literature data on sorption capacity differ by more than one order in magnitude, and the nature of the chemical bonding between GO and metal cations remains unclear. In this work we show that Gd 3+ ions are bound to GO by both coordinate-covalent bonding and electrostatic attraction with prevailing the former. We provide the complete account for the GO sorption toward Gd 3+ as the function of the Gd 3+ /GO ratio and pH of solution. The upper limits of the strong bonding are determined as 0.70 and 0.16 mmol(Gd 3+ )/g(GO) in the neutral and in the intrinsically acidic solutions, respectively. At large excess of Gd 3+ in the neutral solutions, the sorption capacity reaches 1.45 mmol(Gd 3+ )/g(GO). The effectiveness of water, hydrochloric acid and EDTA as desorbing eluents is compared. We experimentally demonstrate the existence of the Gd 3+ concentration gradient within the diffuse layer at the GO/water interface, and its exponential character on the distance from the GO surface. The thickness of the diffuse layer and the position of the slipping plane are estimated. Such characteristics, typical for colloid systems, show that in solutions, GO flakes form distinct phase, even though they are just one atom thick. Copyright © 2018 Elsevier Inc. All rights reserved.

Contrasting the Influence of Cationic Amino Acids on the Viscosity and Stability of a Highly Concentrated Monoclonal Antibody.

PubMed

Dear, Barton J; Hung, Jessica J; Truskett, Thomas M; Johnston, Keith P

2017-01-01

To explain the effects of cationic amino acids and other co-solutes on the viscosity, stability and protein-protein interactions (PPI) of highly concentrated (≥200 mg/ml) monoclonal antibody (mAb) solutions to advance subcutaneous injection. The viscosities of ≥200 mg/ml mAb1 solutions with various co-solutes and pH were measured by capillary rheometry in some cases up to 70,000 s -1 . The viscosities are analyzed in terms of dilute PPI characterized by diffusion interaction parameters (k D ) from dynamic light scattering (DLS). MAb stability was measured by turbidity and size exclusion chromatography (SEC) after 4 weeks of 40°C storage. Viscosity reductions were achieved by reducing the pH, or adding histidine, arginine, imidazole or camphorsulfonic acid, each of which contains a hydrophobic moiety. The addition of inorganic electrolytes or neutral osmolytes only weakly affected viscosity. Systems with reduced viscosities also tended to be Newtonian, while more viscous systems were shear thinning. Viscosity reduction down to 20 cP at 220 mg/ml mAb1 was achieved with co-solutes that are both charged and contain a hydrophobic interaction domain for sufficient binding to the protein surface. These reductions are related to the DLS diffusion interaction parameter, k D , only after normalization to remove the effect of charge screening. Shear rate profiles demonstrate that select co-solutes reduce protein network formation.

Controlled Electrostatic Self-Assembly of Ibuprofen-Cationic Dextran Nanoconjugates Prepared by low Energy Green Process - a Novel Delivery Tool for Poorly Soluble Drugs.

PubMed

Abioye, Amos Olusegun; Kola-Mustapha, Adeola

2015-06-01

The direct effect of electrostatic interaction between ibuprofen and cationic dextran on the system-specific physicochemical parameters and intrinsic dissolution characteristics of ibuprofen was evaluated in order to develop drug-polymer nanoconjugate as a delivery strategy for poorly soluble drugs. Amorphous ibuprofen-DEAE dextran (Ddex) nanoconjugate was prepared using a low energy, controlled amphiphile-polyelectrolyte electrostatic self-assembly technique optimized by ibuprofen critical solubility and Ddex charge screening. Physicochemical characteristics of the nanoconjugates were evaluated using FTIR, DSC, TGA, NMR and SEM relative to pure ibuprofen. The in vitro release profiles and mechanism of ibuprofen release were determined using mathematical models including zero and first order kinetics; Higuchi; Hixson-Crowell and Korsmeyer-Peppas. Electrostatic interaction between ibuprofen and Ddex was confirmed with FT-IR, (1)H NMR and (13)C NMR spectroscopy. The broad and diffused DSC peaks of the nanoconjugate as well as the disappearance of ibuprofen melting peak provided evidence for their highly amorphous state. Low concentrations of Ddex up to 1.0 × 10(-6) g/dm(3) enhanced dissolution of ibuprofen to a maximum of 81.32% beyond which retardation occurred steadily. Multiple release mechanisms including diffusion; discrete drug dissolution; anomalous transport and super case II transport were noted. Controlled assembly of ibuprofen and Ddex produced a novel formulation with potential extended drug release dictated by Ddex concentration.

Effect of Ca substitution on some physical properties of nano-structured and bulk Ni-ferrite samples

NASA Astrophysics Data System (ADS)

Assar, S. T.; Abosheiasha, H. F.

2015-01-01

Nanoparticles of Ni1-xCaxFe2O4 (x=0.0, 0.02, 0.04, 0.06 and 0.10) were prepared by citrate precursor method. A part of these samples was sintered at 600 °C for 2 h in order to keep the particles within the nano-size while the other part was sintered at 1000 °C to let the particles to grow to the bulk size. The effect of Ca2+ ion substitution in nickel ferrite on some structural, magnetic, electrical and thermal properties was investigated. All samples were characterized by using X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometer (VSM). A two probe method was used to measure the dc electrical conductivity whereas the photoacoustic (PA) technique was used to determine the thermal diffusivity of the samples. To interpret different experimental results for nano and bulk samples some cation distributions were assumed based on the VSM and XRD data. These suggested cation distributions give logical explanations for other experimental results such as the observed values of the absorption bands in FTIR spectra and the dc conductivity results. Finally, in the thermal measurements it was found that increasing the Ca2+ ion content causes a decrease in the thermal diffusivity of both nano and bulk samples. The explanation of this behavior is ascribed to the phonon-phonon scattering.

Aquaporins and membrane diffusion of CO2 in living organisms.

PubMed

Kaldenhoff, Ralf; Kai, Lei; Uehlein, Norbert

2014-05-01

Determination of CO2 diffusion rates in living cells revealed inconsistencies with existing models about the mechanisms of membrane gas transport. Mainly, these discrepancies exist in the determined CO2 diffusion rates of bio-membranes, which were orders of magnitudes below those for pure lipid bilayers or theoretical considerations as well as in the observation that membrane insertion of specific aquaporins was rescuing high CO2 transport rates. This effect was confirmed by functional aquaporin protein analysis in heterologous expression systems as well as in bacteria, plants and partly in mammals. This review summarizes the arguments in favor of and against aquaporin facilitated membrane diffusion of CO2 and reports about its importance for the physiology of living organisms. Most likely, the aquaporin tetramer forming an additional fifth pore is required for CO2 diffusion facilitation. Aquaporin tetramer formation, membrane integration and disintegration could provide a mechanism for regulation of cellular CO2 exchange. The physiological importance of aquaporin mediated CO2 membrane diffusion could be shown for plants and cyanobacteria and partly for mammals. Taking the mentioned results into account, consequences for our current picture of cell membrane transport emerge. It appears that in some or many instances, membranes might not be as permeable as it was suggested by current bio-membrane models, opening an additional way of controlling the cellular influx or efflux of volatile substances like CO2. This article is part of a Special Issue entitled Aquaporins. © 2013.

Conjugate gradient filtering of instantaneous normal modes, saddles on the energy landscape, and diffusion in liquids.

PubMed

Chowdhary, J; Keyes, T

2002-02-01

Instantaneous normal modes (INM's) are calculated during a conjugate-gradient (CG) descent of the potential energy landscape, starting from an equilibrium configuration of a liquid or crystal. A small number (approximately equal to 4) of CG steps removes all the Im-omega modes in the crystal and leaves the liquid with diffusive Im-omega which accurately represent the self-diffusion constant D. Conjugate gradient filtering appears to be a promising method, applicable to any system, of obtaining diffusive modes and facilitating INM theory of D. The relation of the CG-step dependent INM quantities to the landscape and its saddles is discussed.

Facilitated transport of small molecules and ions for energy-efficient membranes.

PubMed

Li, Yifan; Wang, Shaofei; He, Guangwei; Wu, Hong; Pan, Fusheng; Jiang, Zhongyi

2015-01-07

In nature, the biological membrane can selectively transport essential small molecules/ions through facilitated diffusion via carrier proteins. Intrigued by this phenomenon and principle, membrane researchers have successfully employed synthetic carriers and carrier-mediated reversible reactions to enhance the separation performance of synthetic membranes. However, the existing facilitated transport membranes as well as the relevant facilitated transport theories have scarcely been comprehensively reviewed in the literature. This tutorial review primarily covers the two aspects of facilitated transport theories: carrier-mediated transport mechanisms and facilitated transport chemistries, including the design and fabrication of facilitated transport membranes. The applications of facilitated transport membranes in energy-intensive membrane processes (gas separation, pervaporation, and proton exchange membrane fuel cells) have also been discussed. Hopefully, this review will provide guidelines for the future research and development of facilitated transport membranes with high energy efficiency.

Cross-linked high amylose starch derivatives for drug release III. Diffusion properties.

PubMed

Mulhbacher, Jérôme; Mateescu, Mircea Alexandru

2005-06-13

Acetate (Ac-), aminoethyl (AE-) and carboxymethyl (CM-) derivatives of cross-linked high amylose starch (HASCL-6) were previously shown to control the release of drugs over 20 h from highly loaded (up to 60% drug) monolithic tablets. This report presents a diffusion analysis, aimed to facilitate a better understanding of the mechanisms involved in the control of the drug release from these hydrogels. The diffusion was found to depend on the molecular weight of the diffusant, whereas the partition coefficient depended on the affinities of the diffusant for the polymers and for the dissolution media via attractive or repulsive ionic interactions. The diffusion was also affected by the swelling of CM-HASCL-6, which, unexpectedly, increased with the decrease of the ionic strength. This diffusion analysis completes the swelling studies of HASCL-6 and of its derivatives, allowing the prediction of release kinetics of various active agents.

Wyman's equation and oxygen flux through the red cell.

PubMed

McCabe, Michael; Maguire, David J

2007-01-01

Wyman's equation of 1966 describes the facilitation of flux of a reversibly bound substrate such as oxygen, consequent on the translational diffusion of the binding protein (the carrier). While Wyman's equation, or some modification of it such as that by Murray 2, may provide a realistic description of the flux of oxygen through a dilute solution of haemoglobin (see also Wittenburg), it is unlikely to be the complete explanation, nor even the basis, for oxygen transport through the intact red cell. The mature erythrocyte contains approximately 350 g/l haemoglobin, and while this suggests that only 35% of the available water volume is actually occupied by the protein, the remaining 65% is unavailable for protein translational diffusion due to the mutual exclusion of the haemoglobin molecules. For this reason we have examined other possible mechanisms whereby haemoglobin may facilitate the translational diffusion of oxygen within the erythrocyte. Possible alternatives include rotational diffusion by the haemoglobins, intracellular shuffling of haemoglobins due to shape changes by the erythrocyte, and haemoglobin rotations and oxygen exchange consequent on the charge change which accompanies substration and desubstration of the haemoglobin molecule. Finally the dipole interactions are shown to generate significant intermolecular attractions between adjacent haemoglobins.

Site identity and importance in cosubstituted bixbyite In 2O 3

DOE PAGES

Rickert, Karl; Harris, Jeremy; Sedefoglu, Nazmi; ...

2017-02-09

The bixbyite structure of In 2O 3 has two nonequivalent, 6-coordinate cation sites and, when Sn is doped into In 2O 3, the Sn prefers the “b-site” and produces a highly conductive material. When divalent/tetravalent cation pairs are cosubstituted into In 2O 3, however, the conductivity increases to a lesser extent and the site occupancy is less understood. We examine the site occupancy in the Mg xIn 2–2xSn xO 3 and Zn xIn 2–2xSn xO 3 systems with high resolution X-ray and neutron diffraction and density functional theory computations, respectively. In these sample cases and those that are previously reportedmore » in the M xIn 2–2xSn xO 3 (M = Cu, Ni, or Zn) systems, the solubility limit is greater than 25%, ensuring that the b-site cannot be the exclusively preferred site as it is in Sn:In 2O 3. Prior to this saturation point, we report that the M 2+ cation always has at least a partial occupancy on the d-site and the Sn 4+ cation has at least a partial occupancy on the b-site. The energies of formation for these configurations are highly favored, and prefer that the divalent and tetravalent substitutes are adjacent in the crystal lattice, which suggests short range ordering. Diffuse reflectance and 4-point probe measurements of Mg xIn 2–xSn xO 3 demonstrate that it can maintain an optical band gap >2.8 eV while surpassing 1000 S/cm in conductivity. Furthermore, understanding how multiple constituents occupy the two nonequivalent cation sites can provide information on how to optimize cosubstituted systems to increase Sn solubility while maintaining its dopant nature, achieving maximum conductivity.« less

Site identity and importance in cosubstituted bixbyite In 2O 3

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rickert, Karl; Harris, Jeremy; Sedefoglu, Nazmi

The bixbyite structure of In 2O 3 has two nonequivalent, 6-coordinate cation sites and, when Sn is doped into In 2O 3, the Sn prefers the “b-site” and produces a highly conductive material. When divalent/tetravalent cation pairs are cosubstituted into In 2O 3, however, the conductivity increases to a lesser extent and the site occupancy is less understood. We examine the site occupancy in the Mg xIn 2–2xSn xO 3 and Zn xIn 2–2xSn xO 3 systems with high resolution X-ray and neutron diffraction and density functional theory computations, respectively. In these sample cases and those that are previously reportedmore » in the M xIn 2–2xSn xO 3 (M = Cu, Ni, or Zn) systems, the solubility limit is greater than 25%, ensuring that the b-site cannot be the exclusively preferred site as it is in Sn:In 2O 3. Prior to this saturation point, we report that the M 2+ cation always has at least a partial occupancy on the d-site and the Sn 4+ cation has at least a partial occupancy on the b-site. The energies of formation for these configurations are highly favored, and prefer that the divalent and tetravalent substitutes are adjacent in the crystal lattice, which suggests short range ordering. Diffuse reflectance and 4-point probe measurements of Mg xIn 2–xSn xO 3 demonstrate that it can maintain an optical band gap >2.8 eV while surpassing 1000 S/cm in conductivity. Furthermore, understanding how multiple constituents occupy the two nonequivalent cation sites can provide information on how to optimize cosubstituted systems to increase Sn solubility while maintaining its dopant nature, achieving maximum conductivity.« less

Method for facilitating catalyzed oxidation reactions, device for facilitating catalyzed oxidation reactions

DOEpatents

Beuhler, Robert J [East Moriches, NY; White, Michael G [Blue Point, NY; Hrbek, Jan [Rocky Point, NY

2006-08-15

A catalytic process for the oxidation of organic. Oxygen is loaded into a metal foil by heating the foil while in contact with an oxygen-containing fluid. After cooling the oxygen-activated foil to room temperature, oxygen diffuses through the foil and oxidizes reactants exposed to the other side of the foil.

The Development and Evaluation of an Information Technology Support System to Facilitate Inter-Organisational Collaboration in HRD

ERIC Educational Resources Information Center

Ford, Norma J.

2006-01-01

Purpose: The purpose of this article is to evaluate the diffusion of and user response to an information technology support system (ITSS) which was designed to facilitate inter-organisational coordination and collaboration in the professional development of officers employed by local authorities (LAs). Design/methodology/approach: An action…

Electrochemistry of Europium(III) Chloride in 3 LiCl – NaCl, 3 LiCl – 2 KCl, LiCl – RbCl, and 3 LiCl – 2 CsCl Eutectics at Various Temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schroll, Cynthia A.; Chatterjee, Sayandev; Levitskaia, Tatiana G.

Here we report the effect of changing the eutectic melt composition on the electrochemical properties of europium(III) chloride under pyroprocessing conditions. The number of electrons transferred, redox potentials and diffusion coefficients were determined using various electrochemical and spectroelectrochemical techniques in four different eutectic mixtures (3 LiCl - NaCl, 3 LiCl - 2 KCl, 3 LiCl - RbCl, and 3 LiCl - 2 CsCl) while varying the temperature of the melt. It was determined that Eu3+ undergoes a one electron reduction to Eu2+ in each melt at all temperatures evaluated. Within all the melts a positive shift in the redox potentialmore » as well as an increase in the diffusion coefficient for Eu3+ was observed as the temperature increased. Also observed was a positive shift in the redox potential and increase in the diffusion coefficient for Eu3+ as the weighted average of the cationic radii for the melt decreased.« less

Equilibrium and kinetic adsorption study of a cationic dye by a natural adsorbent--silkworm pupa.

PubMed

Noroozi, B; Sorial, G A; Bahrami, H; Arami, M

2007-01-02

In this work the use of silkworm pupa, which is the waste of silk spinning industries has been investigated as an adsorbent for the removal of C.I. Basic Blue 41. The amino acid nature of the pupa provided a reasonable capability for dye removal. Equilibrium adsorption isotherms and kinetics were investigated. The adsorption equilibrium data were analyzed by using various adsorption isotherm models and the results have shown that adsorption behavior of the dye could be described reasonably well by either Langmuir or Freundlich models. The characteristic parameters for each isotherm have been determined. The monolayer adsorption capacity was determined to be 555 mg/g. Kinetic studies indicated that the adsorption follows pseudo-second-order kinetics with a rate constant of 0.0434 and 0.0572 g/min mg for initial dye concentration of 200 mg/l at 20 and 40 degrees C, respectively. Kinetic studies showed that film diffusion and intra-particle diffusion were simultaneously operating during the adsorption process. The rate constant for intra-particle diffusion was estimated to be 1.985 mg/g min(0.5).

Retention modeling for ultra-thin density of Cu-based conductive bridge random access memory (CBRAM)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aga, Fekadu Gochole; Woo, Jiyong; Lee, Sangheon

We investigate the effect of Cu concentration On-state resistance retention characteristics of W/Cu/Ti/HfO{sub 2}/Pt memory cell. The development of RRAM device for application depends on the understanding of the failure mechanism and the key parameters for device optimization. In this study, we develop analytical expression for cations (Cu{sup +}) diffusion model using Gaussian distribution for detailed analysis of data retention time at high temperature. It is found that the improvement of data retention time depends not only on the conductive filament (CF) size but also on Cu atoms concentration density in the CF. Based on the simulation result, better datamore » retention time is observed for electron wave function associated with Cu{sup +} overlap and an extended state formation. This can be verified by analytical calculation of Cu atom defects inside the filament, based on Cu{sup +} diffusion model. The importance of Cu diffusion for the device reliability and the corresponding local temperature of the filament were analyzed by COMSOL Multiphysics simulation.« less

Overcharging below the nanoscale: Multivalent cations reverse the ion selectivity of a biological channel

NASA Astrophysics Data System (ADS)

García-Giménez, Elena; Alcaraz, Antonio; Aguilella, Vicente M.

2010-02-01

We report charge inversion within a nanoscopic biological protein ion channel in salts of multivalent ions. The presence of positive divalent and trivalent counterions reverses the cationic selectivity of the OmpF channel, a general diffusion porin located in the outer membrane of E. coli. We discuss the conditions under which charge inversion can be inferred from the change in sign of the measured quantity, the channel zero current potential. By comparing experimental results in protein channels whose charge has been modified after site-directed mutagenesis, the predictions of current theories of charge inversion are critically examined. It is emphasized that charge inversion does not necessarily increase with the bare surface charge density of the interface and that even this concept of surface charge density may become meaningless in some biological ion channels. Thus, any theory based on electrostatic correlations or chemical binding should explicitly take into account the particular structure of the charged interface.

Atomic origins of water-vapour-promoted alloy oxidation

NASA Astrophysics Data System (ADS)

Luo, Langli; Su, Mao; Yan, Pengfei; Zou, Lianfeng; Schreiber, Daniel K.; Baer, Donald R.; Zhu, Zihua; Zhou, Guangwen; Wang, Yanting; Bruemmer, Stephen M.; Xu, Zhijie; Wang, Chongmin

2018-06-01

The presence of water vapour, intentional or unavoidable, is crucial to many materials applications, such as in steam generators, turbine engines, fuel cells, catalysts and corrosion1-4. Phenomenologically, water vapour has been noted to accelerate oxidation of metals and alloys5,6. However, the atomistic mechanisms behind such oxidation remain elusive. Through direct in situ atomic-scale transmission electron microscopy observations and density functional theory calculations, we reveal that water-vapour-enhanced oxidation of a nickel-chromium alloy is associated with proton-dissolution-promoted formation, migration, and clustering of both cation and anion vacancies. Protons derived from water dissociation can occupy interstitial positions in the oxide lattice, consequently lowering vacancy formation energy and decreasing the diffusion barrier of both cations and anions, which leads to enhanced oxidation in moist environments at elevated temperatures. This work provides insights into water-vapour-enhanced alloy oxidation and has significant implications in other material and chemical processes involving water vapour, such as corrosion, heterogeneous catalysis and ionic conduction.

Systematic computational and experimental investigation of lithium-ion transport mechanisms in polyester-based polymer electrolytes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Webb, Michael A.; Jung, Yukyung; Pesko, Danielle M.

Understanding the mechanisms of lithium-ion transport in polymers is crucial for the design of polymer electrolytes. We combine modular synthesis, electrochemical characterization, and molecular simulation to investigate lithium-ion transport in a new family of polyester-based polymers and in poly(ethylene oxide) (PEO). Theoretical predictions of glass-transition temperatures and ionic conductivities in the polymers agree well with experimental measurements. Interestingly, both the experiments and simulations indicate that the ionic conductivity of PEO, relative to the polyesters, is far higher than would be expected from its relative glass-transition temperature. The simulations reveal that diffusion of the lithium cations in the polyesters proceeds viamore » a different mechanism than in PEO, and analysis of the distribution of available cation solvation sites in the various polymers provides a novel and intuitive way to explain the experimentally observed ionic conductivities. This work provides a platform for the evaluation and prediction of ionic conductivities in polymer electrolyte materials.« less

Preparation and Analysis of RNA Crystals

NASA Technical Reports Server (NTRS)

Todd, Paul

2000-01-01

The crystallization of RiboNucleic Acids (RNA) was studied from the standpoint of mechanisms of crystal growth in three tasks: (1) preparation of high-quality crystals of oligonuclotides for X-ray diffraction, (2) finding pathways to the growth of high-quality crystals for X-ray diffraction and (3) investigation of mechanisms of action of inertial acceleration on crystal growth. In these tasks: (1) RNA crystals were prepared and studied by X-ray diffraction; (2) a pathway to high-quality crystals was discovered and characterized; a combination of kinetic and equilibrium factors could be optimized as described below; and (3) an interplay between purity and gravity was found in a combination of space and ground experiments with nucleic acids and proteins. Most significantly, the rate of concentration of precipitant and RNA can be controlled by membrane-based methods of water removal or by diffusion of multivalent cations across an interface stabilized by a membrane. Oligonucleotide solutions are electrokinetically stabilized colloids, and crystals can form by the controlled addition of multivalent cations.

The structure feature of layered M1/3TiNbO5 (M=Fe, Ce) and their photocatalytic oxidization performance for ethyl mercaptan

NASA Astrophysics Data System (ADS)

Dong, Rui; Wang, Yuan; Wang, Ningning; Xu, Lei; He, Jie; Wu, Shanshan; Lan, Yunxiang; Hu, Jinsong

2016-09-01

Layered photocatalytic materials M1/3TiNbO5 (M = Fe, Ce) were prepared by ion-exchange of KTiNbO5 with M(NO3)3. The parent KTiNbO5 was synthesized with titanium (IV) isopropoxide and niobium oxalate by a novel polymerized complex (PC) method. The micro-structures and spectral response features of the as-prepared samples were characterized by powder X-ray diffraction (XRD), transmission electron microscope (TEM), laser Raman spectroscopy (LRS) and UV-vis diffuse reflectance spectroscopy (UV-vis DRS). The results revealed that there was a significant interaction between the interlayer cation and the terminal Nbdbnd O (Tidbnd O) bond in the NbO6 (TiO6) unit of the laminates. Photocatalytic performance was evaluated in oxidation of ethyl mercaptan under natural and UV light irradiation. It can be deduced that the photocatalytic oxidization performance can be directly affected by the characteristics of the interlayer cations.

Microstructure of room temperature ionic liquids at stepped graphite electrodes

DOE PAGES

Feng, Guang; Li, Song; Zhao, Wei; ...

2015-07-14

Molecular dynamics simulations of room temperature ionic liquid (RTIL) [emim][TFSI] at stepped graphite electrodes were performed to investigate the influence of the thickness of the electrode surface step on the microstructure of interfacial RTILs. A strong correlation was observed between the interfacial RTIL structure and the step thickness in electrode surface as well as the ion size. Specifically, when the step thickness is commensurate with ion size, the interfacial layering of cation/anion is more evident; whereas, the layering tends to be less defined when the step thickness is close to the half of ion size. Furthermore, two-dimensional microstructure of ionmore » layers exhibits different patterns and alignments of counter-ion/co-ion lattice at neutral and charged electrodes. As the cation/anion layering could impose considerable effects on ion diffusion, the detailed information of interfacial RTILs at stepped graphite presented here would help to understand the molecular mechanism of RTIL-electrode interfaces in supercapacitors.« less

Effect of polacrilin potassium as disintegrant on bioavailability of diclofenac potassium in tablets : a technical note.

PubMed

Bele, Mrudula H; Derle, Diliprao V

2012-09-01

Polacrilin potassium is an ion exchange resin used in oral pharmaceutical formulations as a tablet disintegrant. It is a weakly acidic cation exchange resin. Chemically, it is a partial potassium salt of a copolymer of methacrylic acid with divinyl benzene. It ionizes to an anionic polymer chain and potassium cations. It was hypothesized that polacrilin potassium may be able to improve the permeability of anionic drugs according to the Donnan membrane phenomenon. The effect of polacrilin potassium on the permeability of diclofenac potassium, used as a model anionic drug, was tested in vitro using diffusion cells and in vivo by monitoring serum levels in rats. The amount of drug permeated across a dialysis membrane in vitro was significantly more in the presence of polacrilin potassium. Significant improvement was found in the extent of drug absorption in vivo. It could be concluded that polacrilin potassium may be used as a high-functionality excipient for improving the bioavailability of anionic drugs having poor gastrointestinal permeability.

Optical Absorptions of Oxygenated Carbon Chain Cations in the Gas Phase

NASA Astrophysics Data System (ADS)

Hardy, F.-X.; Rice, C. A.; Chakraborty, A.; Fulara, J.; Maier, J. P.

2016-06-01

The gas-phase electronic spectra of linear OC4O+ and a planar C6H2O+ isomer were obtained at a rotational temperature of ≈10 K. Absorption measurements in a 6 K neon matrix were followed by gas-phase observations in a cryogenic radiofrequency ion trap. The origin bands of the 1{}2{{{\\Pi }}}u ≤ftarrow X{}2{{{\\Pi }}}g transition of OC4O+ and the 1{}2A{}2 ≤ftarrow X{}2B1 of HCCC(CO)CCH+ lie at 417.31 ± 0.01 nm and 523.49 ± 0.01 nm, respectively. These constitute the first electronic spectra of oxygenated carbon chain cations studied under conditions that are relevant to the diffuse interstellar bands (DIBs), as both have a visible transition. The recent analysis of the 579.5 nm DIB indicates that small carriers, five to seven heavy atoms, continue to be possible candidates (Huang & Oka 2015). Astronomical implications are discussed regarding this kind of oxygenated molecules.

Gas-phase Absorptions of {{\\rm{C}}}_{42}{{\\rm{H}}}_{18}^{+} near 8300 Å below 10 K: Astronomical Implications

NASA Astrophysics Data System (ADS)

Campbell, E. K.; Maier, J. P.

2017-11-01

The gas-phase electronic spectrum of {{{C}}}42{{{H}}}18+ ({{HBC}}+) with an origin band at 8281 \\mathringA has been measured below 10 {{K}} by photofragmentation of helium complexes ({{{C}}}42{{{H}}}18+{--}{{He}}n) in a radiofrequency trap. {{HBC}}+ is a medium-sized polycyclic aromatic hydrocarbon (PAH) cation, and using an ion trapping technique it has been possible to record a high-quality gas-phase spectrum to directly compare with astronomical observations. No diffuse interstellar bands (DIBs) have been reported at the wavelengths of the strongest absorption bands in the {{{C}}}42{{{H}}}18+ spectrum. Measurement of absolute absorption cross sections in the ion trap allows upper limits to the column density of this ion to be {10}12 {{cm}}-2, indicating that even PAH cations of this size, which are believed to be stable in the interstellar medium, should be excluded as candidates for at least the strong DIBs.

A2TiF 5· nH 2O ( A=K, Rb, or Cs; n=0 or 1): Synthesis, structure, characterization, and calculations of three new uni-dimensional titanium fluorides

NASA Astrophysics Data System (ADS)

Jo, Vinna; Woo Lee, Dong; Koo, Hyun-Joo; Ok, Kang Min

2011-04-01

Three new uni-dimensional alkali metal titanium fluoride materials, A2TiF 5· nH 2O ( A=K, Rb, or Cs; n=0 or 1) have been synthesized by hydrothermal reactions. The structures of A2TiF 5· nH 2O have been determined by single-crystal X-ray diffraction. The Ti 4+ cations have been reduced to Ti 3+ during the synthesis reactions. All three A2TiF 5· nH 2O materials contain novel 1-D chain structures that are composed of the slightly distorted Ti 3+F 6 corner-sharing octahedra attributable to the Jahn-Teller distortion. The coordination environment of the alkali metal cations plays an important role to determine the degree of turning in the chain structures. Complete structural analyses, Infrared and UV-vis diffuse reflectance spectra, and thermal analyses are presented, as are electronic structure calculations.

Systematic computational and experimental investigation of lithium-ion transport mechanisms in polyester-based polymer electrolytes

DOE PAGES

Webb, Michael A.; Jung, Yukyung; Pesko, Danielle M.; ...

2015-07-10

Understanding the mechanisms of lithium-ion transport in polymers is crucial for the design of polymer electrolytes. We combine modular synthesis, electrochemical characterization, and molecular simulation to investigate lithium-ion transport in a new family of polyester-based polymers and in poly(ethylene oxide) (PEO). Theoretical predictions of glass-transition temperatures and ionic conductivities in the polymers agree well with experimental measurements. Interestingly, both the experiments and simulations indicate that the ionic conductivity of PEO, relative to the polyesters, is far higher than would be expected from its relative glass-transition temperature. The simulations reveal that diffusion of the lithium cations in the polyesters proceeds viamore » a different mechanism than in PEO, and analysis of the distribution of available cation solvation sites in the various polymers provides a novel and intuitive way to explain the experimentally observed ionic conductivities. This work provides a platform for the evaluation and prediction of ionic conductivities in polymer electrolyte materials.« less

Understanding Tribofilm Formation Mechanisms in Ionic Liquid Lubrication

DOE PAGES

Zhou, Yan; Leonard, Donovan N.; Guo, Wei; ...

2017-08-16

Ionic liquids (ILs) have recently been developed as a novel class of lubricant anti-wear (AW) additives, but the formation mechanism of their wear protective tribofilms is not yet well understood. Unlike the conventional metal-containing AW additives that self-react to grow a tribofilm, the metal-free ILs require a supplier of metal cations in the tribofilm growth. The two apparent sources of metal cations are the contact surface and the wear debris, and the latter contains important ‘historical’ interface information but often is overlooked. We correlated the morphological and compositional characteristics of tribofilms and wear debris from an IL-lubricated steel–steel contact. Inmore » conclusion, a complete multi-step formation mechanism is proposed for the tribofilm of metal-free AW additives, including direct tribochemical reactions between the metallic contact surface with oxygen to form an oxide interlayer, wear debris generation and breakdown, tribofilm growth via mechanical deposition, chemical deposition, and oxygen diffusion.« less

Hydrodynamic interpretation on the rotational diffusion of peroxylamine disulfonate solute dissolved in room temperature ionic liquids as studied by electron paramagnetic resonance spectroscopy.

PubMed

Miyake, Yusuke; Akai, Nobuyuki; Kawai, Akio; Shibuya, Kazuhiko

2011-06-23

Rotational motion of a nitroxide radical, peroxylamine disulfonate (PADS), dissolved in room temperature ionic liquids (RTILs) was studied by analyzing electron paramagnetic resonance spectra of PADS in various RTILs. We determined physical properties of PADS such as the hyperfine coupling constant (A), the temperature dependence of anisotropic rotational correlation times (τ(∥) and τ(⊥)), and rotational anisotropy (N). We observed that the A values remain unchanged for various RTILs, which indicates negligible interaction between the N-O PADS group and the cation of RTIL. Large N values suggest strong interaction of the negative sulfonyl parts of PADS with the cations of RTILs. Most of the τ(∥), τ(⊥), and (τ(∥)τ(⊥))(1/2) values are within the range calculated on the basis of a hydrodynamic theory with stick and slip boundary conditions. It was deduced that this theory could not adequately explain the measured results in some RTILs with smaller BF(4) and PF(6) anions.

Systematic Computational and Experimental Investigation of Lithium-Ion Transport Mechanisms in Polyester-Based Polymer Electrolytes

PubMed Central

2015-01-01

Understanding the mechanisms of lithium-ion transport in polymers is crucial for the design of polymer electrolytes. We combine modular synthesis, electrochemical characterization, and molecular simulation to investigate lithium-ion transport in a new family of polyester-based polymers and in poly(ethylene oxide) (PEO). Theoretical predictions of glass-transition temperatures and ionic conductivities in the polymers agree well with experimental measurements. Interestingly, both the experiments and simulations indicate that the ionic conductivity of PEO, relative to the polyesters, is far higher than would be expected from its relative glass-transition temperature. The simulations reveal that diffusion of the lithium cations in the polyesters proceeds via a different mechanism than in PEO, and analysis of the distribution of available cation solvation sites in the various polymers provides a novel and intuitive way to explain the experimentally observed ionic conductivities. This work provides a platform for the evaluation and prediction of ionic conductivities in polymer electrolyte materials. PMID:27162971

Atomic origins of water-vapour-promoted alloy oxidation.

PubMed

Luo, Langli; Su, Mao; Yan, Pengfei; Zou, Lianfeng; Schreiber, Daniel K; Baer, Donald R; Zhu, Zihua; Zhou, Guangwen; Wang, Yanting; Bruemmer, Stephen M; Xu, Zhijie; Wang, Chongmin

2018-06-01

The presence of water vapour, intentional or unavoidable, is crucial to many materials applications, such as in steam generators, turbine engines, fuel cells, catalysts and corrosion 1-4 . Phenomenologically, water vapour has been noted to accelerate oxidation of metals and alloys 5,6 . However, the atomistic mechanisms behind such oxidation remain elusive. Through direct in situ atomic-scale transmission electron microscopy observations and density functional theory calculations, we reveal that water-vapour-enhanced oxidation of a nickel-chromium alloy is associated with proton-dissolution-promoted formation, migration, and clustering of both cation and anion vacancies. Protons derived from water dissociation can occupy interstitial positions in the oxide lattice, consequently lowering vacancy formation energy and decreasing the diffusion barrier of both cations and anions, which leads to enhanced oxidation in moist environments at elevated temperatures. This work provides insights into water-vapour-enhanced alloy oxidation and has significant implications in other material and chemical processes involving water vapour, such as corrosion, heterogeneous catalysis and ionic conduction.